Actually, I think it's kind of a missed opportunity.
Sinister should have been the main Villain in a pre-Apocalypse movie. This way they could plan for 2 additional X-Men movies and not just go right into Apocalypse.
This way Sinister could be the main villain with his Marauders as the guys that get defeated in battle with the new X-Men. At the end of the movie Sinister's relation to Gambit and/or Apocalypse could have been shown to set up the Apocalypse movie.
Tryng to cram Mr. Sinister, who has an amazing backstory which would deserve to be told, into a movie with Apocalypse, would be too much, which means, unfortunately, I can't see him making it, unless they change something significant. They would need to make this 2 movies, or give Sinister his own...
Actually, here is a posting (slightly updated) to a thread of mine focusing on what I would love to see for a pre-Apocalypse Sinister as the main villain movie:
If they want the next movie with the "First Class" (I hate refering to them like that), back in the 80's, then why not focus on Mister Sinister as a lead in to Apocalypse? The movie could start off back in the mid-1800's and focus on a doctor named Nathaniel Essex and show his obsession with the theories of Darwin. It could be shown how he presented his theories of how Humanity will mutate and how his colleagues mocked him and his theories. It could be shown how he had a group called the Marauders (a bunch of thugs) collect test subjects, and how his son died and he performed tests on his corpse. His wife finds out and frees all of the test subjects. Essex asks for forgiveness and she states “To me, you are... utterly… and contemptibly… sinister!”. She then dies and we fade out to start back in the 1980's at the X-Mansion.
In the 80's the whole Mutant Massacre storyline could be played out with the Marauders as the group the young X-Men (young Scott, young Jean, young Ororo, young Nightcrawler, Gambit and maybe Beast) must fight, and Sinister as the one pulling all the strings. Since this would be in the 80's Gambit could be used. Sabertooth could be as well, and for the other Marauders a good list would be:
Harpoon
Vertigo
Scalphunter
Riptide
Scrambler
So effectively the Mutant Massacre story plays out in the mid 80's, missing a few bits of canon, such as Leech or Angel losing his wings, due to the continuity issues. Obviously no Thor or X-Factor.
Some of the Morlocks could be as follows:
Caliban
Marrow
Masque
Annalee
Ape
Healer
Artie
Feral
Sunder
Etc.
Obviously you wouldn't get into each and every one, but say Feral, Caliban and Marrow would be good to meet. At the climax many would, of course, be massacred...
The X-Men would take down the Marauders, some excaping, some not being so lucky, and ultimately Sinister (who would now be known to the GA) would have gotten what he wanted, a strengthening of the gene pool, and would be available to serve En Sabur Nur in the dystopian future where he belongs.
Now this concept of mine would be perfect as a set up to the Apocalypse movie, but again, since the movie title has already been announced, I think we're not going to get this.
Maybe Mr. Sinister will end up being in the Deadpool movie, similar to the video game?
Man, what a missed opportunity!!!