The only restrictions are:
1) Actor must be alive
2) Actor must have an imdb page
3) Actor must not already be cast in Silm Film (exceptions made for voice roles)
We've cast actors who no longer work in film before. I know the actor we chose for Sauron has transitioned to writing stage plays and raising children, and expressed frustration with the industry (so would be unlikely to show interest in a long-term TV role). We work on the assumption that we could tempt them out of retirement with our awesome project.
We've cast actors who have never worked in television before, or who cost $1 million dollars to hire for a movie. In the real world, that would not happen, but in 'fantasy casting', it's fine. If we want Dwayne 'The Rock' Johnson to play Tulkas, then we can say so.
If an actor's illness or injury means that they no longer are capable of working, I recognize that it might seem insensitive to suggest them for a role. Or, it could be a tribute to their past work, since their current illness does not actually prevent them from starring in our fake show. That is probably something that can be handled on a case by case basis. It's something to discuss here, but is not a barrier to nomination.
If an actor is considered problematic because of their personal life, public statements, criminal activity, or a history of being difficult to work with, etc, certainly that can be a reason to choose not to nominate him or her for a role. It does not automatically disqualify them, though. Because choosing them is NOT giving them a job. One reason is that this fan project is small in scope, so it would generate neither funds, press, attention, nor anything else of value to the actor in question. So, since we are doing no harm, there is no rule against selecting someone with a bad past. If I hate an actor's body of work, I'm not going to nominate them for anything, though.
I have no idea what Shia LeBoeuf has done to make him unhireable right now; I was unaware that there was any issue there. (I assume he's not actually a murderous cannibal...) According to imdb, he portrays Padre Pio in a 2022 film. That is in part why I suggested him - if he was hired to play an Italian, he probably fits the bill of 'Mediterranean looks' that will work with the other cast members in the House of Bëor.
But to state this as plainly as I can: 85-year-old Bill Cosby is eligible to be cast on Silm Film for the remainder of his life. I don't foresee any role where people are going to say, 'Man, you know who would be perfect for that? Bill Cosby!' And if it did come up, I would likely refrain from nominating him myself, because the first thing I think of when I hear his name now is not his long career as
a comedian and actor, but the court cases related to him drugging women. So...that's fine. But he is eligible, so if someone does wish to nominate him (say, for a voice role), they're allowed.