I agree that doing AoA wouldn't make much sense, especially not after a movie involving time travel and alternate realities in the first place. (I also think the AoA storyline is overrated and mostly gets a pass for a) the cool factor and b) Blink.) But Apocalypse's origin doesn't have to involve any of the wankery his comic origin offers. Just have him be an ancient, really powerful mutant who wants to ignite a war not just between humans and mutants, but mutants and mutants, until only the strongest are left. In fact, he could be the big bad pulling the strings in DoFP, which lets that movie set up the next one.