I think this all comes down to the actors that we have. Once the current actors for Xavier and Magneto, and especially Jean and Wolvie are no longer going to be used, it will be time to reboot or go in a different direction. Knowing that these movies come out say every three years that would mean that the next X-Men movie is likely for 2017...
I think all of us would agree with you that Apocalypse is the biggest threat possible in the X-Men stories. So this begs the question:
- With the current actors and the current X-Men movie universe, is X5, which will likely be in 2017, the last one? If so then doesn't AOA make sense?
If not then I can see what you're saying. I've always thought that a Mutant Massacre movie would be great, with the Reavers as the main bad guys and Sinister as the force behind them. And then that would lead to a Sinister movie.
So yes, if they want to have movies in between DOFP and AOA then have Wolvie come back, everything is "fixed" and Jean and Scott are back. great. Then have a movie or two inbetween. And then have someone (Legion or someone else) go back in time again, accidentally kil Xavier, which causes the AOA.
My thought is that too many go back in time movies will come off as "been there, done that". But by having one "go back in time movie" cause the second, "have to go back and fix the past movie", then it seems like one big movie spilt into two...