Credits scene – Mister Sinister setup and more?

Lastly – and this isn’t in any way a question that has no answer – the post-credits scene obviously says that Mister Sinister will be the villain of the next X-Men installment. However, I believe that it will be more than that and he will appear in several other movies in this shared universe instead of just one.
Gambit (whenever it will happen) is also rumored to feature him. Furthermore, the last Wolverine flick starring Hugh Jackman is also rumored to have Mister Sinister appear in one way or another.
There is a question about this, nonetheless – is the credits scene hinting that X-23 will replace the no-nonsense mutant? Everybody believes that it will be so. And it is interesting to see what role this new mutant (if she appears at all) will have in the shared universe.
Thus far, these are the biggest unanswered questions of X-Men: Apocalypse.
Obviously, more could be said – but this would mean nitpicking. Maybe some other time. What do you think? Are there any other big questions to be asked?
