The point Corey Olsen made was that in Season 7, which will be all about the Nirnaeth, we are going to have adult Huor and Húrin from early on. Their adventures in Gondolin as teens would be an episode 1 situation, immediately followed by a time skip bringing us up to date with adult Huor and Húrin in Episode 2. So, where's Galdor? Welcoming them back home to Dor-lomin in a single scene, probably at the end of the first episode of Season 7.
...at least, that's what we have for now. I should point out that we're still trying to plan Season 5, so a lot could change before we actually get to planning Season 7! So, that's a suggestion for now.
For Season 5, what we currently have is:
Episode 1 - A-plot: Bëor-centric. Bëor and company enter Beleriand by crossing the mountains. They hope to find...what? And instead, they meet Finrod. Harp, singing, etc. Bëor pledges himself to Finrod and goes with him to Nargothrond(?) The rest of his people hang out in Estolad.
B-plot: ?? Aredhel in Gondolin or Fingolfin working on the Siege
C-plot: ?? Finrod discusses Men with Thingol
Episode 2 - A-plot: Green-elves are unhappy with all these Men entering Ossiriand. Galadriel and Celeborn help smooth things over. People of (Hador) wind up in Estolad, People of (Haleth) end up in Thargelion. None of them are in Ossiriand, so the Green-elves are happy!
B-plot: ?? Aredhel in Gondolin or Fingolfin working on the Siege
C-plot: ??
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Episode 7 - A-plot: Death of Bëor from old age
B-plot: Athrabeth - Finrod and Aredhel discuss the relationship of Elves and Men, and the differing fates of each people.
C-plot:
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Episode 12 - Dagor Bragollach!
Episode 13 - Aftermath of battle and Fingolfin's duel with Morgoth
Chances are *very* strong that we will revisit the content of Episode 7 after the other storylines get more developed! But in general, we have some concept of how the season will begin and end, so that's likely enough to get started with.
Does every plot line have to follow the theme? The Sindarin plot for Season 3 did not coincide with the theme of Rebellion.
No, not every plotline has to follow the theme. But the more that don't, the more disjointed the Season will become. Season 3 has a very unusual structure, and it would certainly puzzle the audience as to why we're suddenly switching to entire different groups of people as our characters. Season 5 will likely start to feel 'random', like we're just tossing a bunch of disjointed stories together, precisely because some plotlines are isolated and unrelated to the Season's theme. Let's...try our best to relate storylines to the theme when possible!
I think it's best for them to arrive in season 6 because all of that really sets up for the Beren and Lúthien-story that is season 6. I'm in favor of showing Celegorm and Curufin escape from the Bragollach at the end of this season (because it's part of the Noldor losing), but showing them arrive in Nargothrond next season. Also having Sauron take Minas Tirith next season. I think all of it would feel a bit out of place this season. The story this season is really about Finrod and his relationship with men, and Fingolfin and his decision to battle Morgoth, so setting up family drama in Nargothrond at the end would feel a little weird maybe. It could be done, but I also feel that starting with Celegorm and Curufin arriving in Nargothrond and Sauron taking Minas Tirith would be a nice reminder of where these people are since these are the most important (noldo) characters in season 6. It would give them more focus instead of jamming all of it into the battle scenes of episode 13 this season.
Yes, I agree that 'Celegorm and Curufin are in Nargothrond' is a very important plot point for Season 6, and not terribly relevant to Season 5. For Season 5, Celegorm and Curufin are fairly minor characters (having a bit role in Aredhel's story), but other than showing their survival and fleeing from East Beleriand, there's no need for 'starting' a new story for them in the Season finale.
Now, many TV shows *do* start their plot for the next season in the season finale. They want to show enough to get you intrigued, hooked enough to really want to know what happens next! So, some teasers and hooks and previews could be appropriate. But. We don't want to start telling that story yet. We will need to establish those two in Nargothrond in Season 6 anyway, so better to do it then, rather than as a 'refresher' repeating information the audience already knows.
I don't know if for example Meril, Finduilas and Celebrimbor are the most important characters when they arrive in Nargothrond. That would certainly be Orodreth, Celegorm and Curufin (as well as Finrod). Celebrimbor would maybe get more attention when Lúthien arrives in Nargothrond. And Finduilas maybe even later when Túrin comes along. So far I don't really see what will happen to Meril. Was Meril an important character last season? If not maybe she would become more prominent during Orodreth's reign.
Meril was important enough to have lines last season, but I wouldn't necessarily label her important. She is Orodreth's supportive wife, and their marriage was part of the 'Noldor and Sindar reconciliation' arc for the season. Finduilas is shown as a young child in the end-of-season montage. Meril's ultimate fate has not yet been decided. She is going to be Gil-galad's mother at some point.