You have to remember how massive the story lines were for Apocalypse. Having just one movie or three rather would not do the story line justice. I beleive as a reader of all the comics uncanny through to xmen blue team that the movies should surround single events. The classic action genre. A nemesis and a solution utilizing every characters abilities on a smaller scale as to not sell any one character short thus eliminating pissed off fans.
Although......I would love to see the Executioner's song story line on film.....Stryfe and cable, bishop, wolverine, all the x teams, reaper, mister sinister.....damn that's hot