I'm more interested in a sequel (X5, if DoFP is X4) with OT cast set after DoFP future timeline than a 90's movie. Apocalypse didn't leave me wanting more AND I don't want another movie if Kinberg is the screenwriter.
A movie with Cyclops, Jean, Storm, Beast, Wolverine, Rogue and Xavier as the core team, post DoFP, with Kitty, Colossus and Iceman in supporting roles. Add whoever they want to add but don't make them background characters, please.
Villain: Cassandra Nova, whom I think is an underrated villain. She wiped out Genosha with Sentinels, infiltrated the Shi'ar, and nearly defeated the X-Men all on her own. She is a one man army and more menacing than Apocalypse ever was. If you don't know her check out Grant Morrison's "E is for Extinction" and Joss Whedon's last Astonishing X-Men arc. A female villain would be great to see.
I would cast Glenn Close, she has a creepy angular jawed face/smile. She was also amazing on "Damages" .. conniving, intelligent with slight sociopath tendencies. She has great screen presence and will hold her own against Patrick Stewart.