1st thing is a new director ( please, no more 
Ratner) ... someone who is
doesn't have an interest in pushing/rushing the movie to a quick end
and has a knack for developing character and can bring out the 
drama and heartfelt emotions of a film ( i.e. the Xavier mourning was so  ridiculously dim, rushed and emotionless ) ..... the next Xmen 4 film should definitely feature 
GAMBIT  - makes no sense not to have included 
him in four films ths far, ....
 
they may need to consider another villain(s) other than 
Magneto/Mystique , just to add more variety and the danger of being burnout and non-creative..... perhaps maybe a 
cameo by those two  at best, but other villains have to be developed and brought much more attention to...
 
APOCALYPSE is simply the best idea for a new villain. 
(Powerful, murderous, merciless and totally insane.) 
much more than Magneto- they should put the greatest focus 
on him than any other villain ....
 
i can see involving the Sentinels but not an entire movie based on them... i'd involve just ONE or TWO as experiment projects to come after Mutants ( even with Apocalypse "disguised "  in human form as one of the major authorities in charge of the Sentinel- program ) 
 
more of the Kitty/Rogue/Iceman love-hate triangle ( which was another thing rushed and screwed up by 
Ratner terribly in this film) 
i didn't get enough feel for 
Rogue's pain and frustration of being indifferent and not being able to touch/kiss Bobby. 
 
between Apocalypse/Sentinel clashes this next film should based off  the search for 
XAVIER , ... 
i'm optional about bringing back 
Cyclops and 
jean 
i think this can be a successful Xmen without the two of them 
but we simply cannot lose 
WOLVERINE or 
STORM. 
 
