In other words, there is a difference between 'it just never happened' and there being rules saying 'it's strictly forbidden.' We're trying to figure out how to tell our story, how to show character motivations.
We know why the Numenoreans adopted the rule about Ruling Queens; we don't know if the Noldor would ever have done so. There really aren't going to be many stories where it is relevant - I'm thinking most of the story of Maeglin, who more-or-less sees himself as Turgon's heir (or would be, if Idril married him). The real place it matters, though, is in Galadriel's story. Galadriel winds up distancing herself from the Noldor. She moves to Doriath, becomes a pupil of Melian, and marries Celeborn. We know that one of her ambitions in leaving Valinor was to have a realm of her own (which happened in Lothlorien). Was her ambition frowned upon by the Noldor - so that her brother could found Nargothrond, but if she tried to do so, it wouldn't have worked? Is it possible that under no circumstances would the Noldor have accepted the concept of a Ruling Queen? Sure. It's one possible interpretation of the text that such an idea was foreign or unthinkable to them. It's just that it's not the only possible reading, so we were exploring alternatives that maintain what we do know about Noldoran High Kings without relying on that as a codified rule.
Keep in mind that 'oldest of the descendants of Finwë' is going to be Maedhros after Fingolfin's death. Getting Maedhros to agree that Fingon should be High King isn't too difficult. But we do have to be cautious with how we codify that rule. If Fingolfin is the oldest of the descendants of Finwë, and then Fingon is the oldest of the descendants of Fingolfin, that neatly cuts out the Fëanorean branch. But...then why Turgon? Why go back to 'oldest of the descendants of Fingolfin' when you're looking for Fingon's heir? And if you do exhaust the supply of descendants of Fingolfin, and go back to 'descendants of Finwë' when looking for Turgon's heir...that would make the Fëanorean branch of the family eligible again. Maedhros ceded to Fingolfin's claim, and we know that neither he nor any other Fëanorean ever became High King of the Noldor. But that doesn't mean that we can ignore them in the succession - we can't be sure that Maedhros would have ceded to Gil-galad's claim, for instance.
Unless, of course, Gil-galad becomes High King after the War of Wrath, in which case Maedhros is dead and Maglor is gone, leaving only Celebrimbor, whom we *know* acknowledged his High Kingship. As long as that makes sense in our story, we're alright.
Whether or not the Noldor had laws of succession is an open question. If they were a medieval human society, we would not only assume that they do, but have certain assumptions about what those rules would have to be. Preference for male, preference for the younger generation (rather than a brother or uncle), preference for older sons. But with elves, some of those assumptions don't seem to have a basis in the story. We are worldbuilding, here, so need to create rules that make sense for the situation the elves are in. Without a concept of 'old age', would they land on the same inheritance rules the kings of France did? For a culture embroiled in war, the 'but elves are immortal!' rule falls away - any High King could be killed in battle. So, having a plan for an heir can happen, and a preference for male heirs might make sense in that context. What is much iffier is the whole 'firstborn son' concept. Why? Why would they do that? Fëanor had a feud with his younger half-brothers, but the basis of that feud doesn't repeat in later families.
Certainly, the way the texts are written, the narrator assumes the concept of inheritance is understood. It seems natural that a king would have heirs, and it's not all that surprising that Fëanor named his eldest son 'Third Finwë' just to spitefully point out that Fingolfin isn't part of the line of succession, not being a 'true' son of Finwë. That was in Valinor, where no one ever had any reason to think that Finwë would someday die and need an heir. So, did they just come up with some rules of what would happen if Finwë were ever to step down or retire? Was that a thing kings could do? Was there some sort of ceremonial significance to being a king's heir that would not require the death of said king to be meaningful? Tolkien was certainly familiar with succession conflicts in European history and wrote some into his own stories (specifically with stories of Men: when an estranged king and queen of Numenor had only one daughter, Ar-Pharazon unlawfully seizing the throne after his marriage to Míriel, Arvedui's unsuccessful bid to claim the throne of Gondor, the Kinstrife, and even Eomer's inheritance from Thingol his uncle after the king's son Theodred died in battle, etc). But...does any of this make sense for immortal elves who can be slain? Assuring an heir you can pass everything on to is key to any mortal institution or endeavor, because none of us live very long. If you don't make some provision to pass the torch, your accomplishments end and die with you. But why would elves need that concept of 'heir'? I think that's a question our story should answer, even if the texts do not directly address that.
But with elves...why should they immediately go to male primogeniture? It took a lot of specific cases for humans to hammer out inheritance laws, and other than the distinction between children and adults, elves probably don't care overly much about age. There was no harm in having a king's brother inherit, as he would be just as likely to live as long as his son. Whereas when Fidel Castro named his brother as his heir, the world looked at him funny. Likewise with there being no problem with your great-grand-nephew being your heir. The general reasoning for not selecting a female as king is that you want your king to be able to lead the military, to be in the field during a battle. And certainly that is a concern for the Noldor during the First Age. Laws and Customs of the Eldar suggest that young unmarried women can be warriors, but that it would be unusual for a married woman with kids to participate in a battle.
Basically, I'm interested in thinking through the cultural logic of adopting Salic succession laws before assuming that the Noldor have done so. And I want to think about how whatever choices we make play out in our story, how we will present that to the audience.
We know why the Numenoreans adopted the rule about Ruling Queens; we don't know if the Noldor would ever have done so. There really aren't going to be many stories where it is relevant - I'm thinking most of the story of Maeglin, who more-or-less sees himself as Turgon's heir (or would be, if Idril married him). The real place it matters, though, is in Galadriel's story. Galadriel winds up distancing herself from the Noldor. She moves to Doriath, becomes a pupil of Melian, and marries Celeborn. We know that one of her ambitions in leaving Valinor was to have a realm of her own (which happened in Lothlorien). Was her ambition frowned upon by the Noldor - so that her brother could found Nargothrond, but if she tried to do so, it wouldn't have worked? Is it possible that under no circumstances would the Noldor have accepted the concept of a Ruling Queen? Sure. It's one possible interpretation of the text that such an idea was foreign or unthinkable to them. It's just that it's not the only possible reading, so we were exploring alternatives that maintain what we do know about Noldoran High Kings without relying on that as a codified rule.
Keep in mind that 'oldest of the descendants of Finwë' is going to be Maedhros after Fingolfin's death. Getting Maedhros to agree that Fingon should be High King isn't too difficult. But we do have to be cautious with how we codify that rule. If Fingolfin is the oldest of the descendants of Finwë, and then Fingon is the oldest of the descendants of Fingolfin, that neatly cuts out the Fëanorean branch. But...then why Turgon? Why go back to 'oldest of the descendants of Fingolfin' when you're looking for Fingon's heir? And if you do exhaust the supply of descendants of Fingolfin, and go back to 'descendants of Finwë' when looking for Turgon's heir...that would make the Fëanorean branch of the family eligible again. Maedhros ceded to Fingolfin's claim, and we know that neither he nor any other Fëanorean ever became High King of the Noldor. But that doesn't mean that we can ignore them in the succession - we can't be sure that Maedhros would have ceded to Gil-galad's claim, for instance.
Unless, of course, Gil-galad becomes High King after the War of Wrath, in which case Maedhros is dead and Maglor is gone, leaving only Celebrimbor, whom we *know* acknowledged his High Kingship. As long as that makes sense in our story, we're alright.
Whether or not the Noldor had laws of succession is an open question. If they were a medieval human society, we would not only assume that they do, but have certain assumptions about what those rules would have to be. Preference for male, preference for the younger generation (rather than a brother or uncle), preference for older sons. But with elves, some of those assumptions don't seem to have a basis in the story. We are worldbuilding, here, so need to create rules that make sense for the situation the elves are in. Without a concept of 'old age', would they land on the same inheritance rules the kings of France did? For a culture embroiled in war, the 'but elves are immortal!' rule falls away - any High King could be killed in battle. So, having a plan for an heir can happen, and a preference for male heirs might make sense in that context. What is much iffier is the whole 'firstborn son' concept. Why? Why would they do that? Fëanor had a feud with his younger half-brothers, but the basis of that feud doesn't repeat in later families.
Certainly, the way the texts are written, the narrator assumes the concept of inheritance is understood. It seems natural that a king would have heirs, and it's not all that surprising that Fëanor named his eldest son 'Third Finwë' just to spitefully point out that Fingolfin isn't part of the line of succession, not being a 'true' son of Finwë. That was in Valinor, where no one ever had any reason to think that Finwë would someday die and need an heir. So, did they just come up with some rules of what would happen if Finwë were ever to step down or retire? Was that a thing kings could do? Was there some sort of ceremonial significance to being a king's heir that would not require the death of said king to be meaningful? Tolkien was certainly familiar with succession conflicts in European history and wrote some into his own stories (specifically with stories of Men: when an estranged king and queen of Numenor had only one daughter, Ar-Pharazon unlawfully seizing the throne after his marriage to Míriel, Arvedui's unsuccessful bid to claim the throne of Gondor, the Kinstrife, and even Eomer's inheritance from Thingol his uncle after the king's son Theodred died in battle, etc). But...does any of this make sense for immortal elves who can be slain? Assuring an heir you can pass everything on to is key to any mortal institution or endeavor, because none of us live very long. If you don't make some provision to pass the torch, your accomplishments end and die with you. But why would elves need that concept of 'heir'? I think that's a question our story should answer, even if the texts do not directly address that.
But with elves...why should they immediately go to male primogeniture? It took a lot of specific cases for humans to hammer out inheritance laws, and other than the distinction between children and adults, elves probably don't care overly much about age. There was no harm in having a king's brother inherit, as he would be just as likely to live as long as his son. Whereas when Fidel Castro named his brother as his heir, the world looked at him funny. Likewise with there being no problem with your great-grand-nephew being your heir. The general reasoning for not selecting a female as king is that you want your king to be able to lead the military, to be in the field during a battle. And certainly that is a concern for the Noldor during the First Age. Laws and Customs of the Eldar suggest that young unmarried women can be warriors, but that it would be unusual for a married woman with kids to participate in a battle.
Basically, I'm interested in thinking through the cultural logic of adopting Salic succession laws before assuming that the Noldor have done so. And I want to think about how whatever choices we make play out in our story, how we will present that to the audience.