He is a villain sure ,but he cannot carry a 'brotherhood' ,in a way that Magneto did. Sinister doesn't care about mutantdom IXM/SoS was a classic example of what mutants mean to him. I mean it is possible to reinvent the villain by focusing solely on 'Enigma' as a disembodied presence(like Shadowking) pushing for some way to get corporeal form, but other than the old Sinister is a better species/transhumanism spiel, it's no different than Enigma becoming a god. To me the most interesting thing about Sinister in the Krakoa era came right at the end with the recent reveal of Stasis being behind the Vault project and I actually expressed this idea in an old thread when I thought Sinister prime in life 9 created or accessed the vault and the one who was executed by machines was just a clone(making him and the children a possible menace crossing over from life 9 into life 10). Anyway I just think we need some breather from the Sinister centric storylines.
Exodus has a lot of potential , his worldview and ethos representing a quest for a 'golden age' actually means depending on perspective ,he is not necessarily a villain(although he could make a great one) With an enriched backstory,(Gillen had an opportunity to craft it and failed imo) we could see a more complex character than Eric, but I doubt it will happen anytime soon. As for the red colour I actually think it is the only conspicuous mark of his x-gene, but in all other respects at a cursory viewing he is as human as mutants come. His backstory as a warrior for human kings, combined with knowledge of how much has/hasn't changed since then would make for very interesting public addresses.