Who and what I'd like to see in an X4...
I felt X3 was not very good, but I'd like to see more x-films (hopefully better than X3)...
X4
X-Men:
Professor X (the team goes to Muir Island to retrieve him, once they discover he's alive), Storm, Wolverine, Iceman, Nightcrawler (If Alan Cumming doesn't want the part...Replace him.), Rogue (the cure isn't permanent), Kitty, Beast, Colossus...And maybe...Gambit (blech!...I can't stand him, but lot's of folks are hoping he'll be in the next X-film).
Villains:
Mystique (Again: The cure isn't permanent)...She creates an all-new Brotherhood, with the Blob, Toad, Avalanche and Destiny.
The Sentinels and Proteus (evil mutant son of Moira MacTaggart...The Brotherhood could be out to recruit him) and the Sentinels are sent by the US government to hunt down the Brotherhood...And the X-Men can become the robots' targets too.
X5
Villains: Mr Sinister, the Legacy virus and Apocalypse?
X6
Villains: Magneto returns or maybe Apocalypse?