Originally Posted by ThePhantasm
This is just random speculation, but:
Let's assume that DOFP undoes the "old" X-Men films and establishes a new timeline, with the previous timeline contradictions erased. This would open the way to connect the X-Men and Avengers franchises. There would no longer be a chronological contradiction between the two franchises.
Quicksilver could be a brief cameo at the end of the film that basically establishes that this is a new timeline connected to the MCU.
I'm all for that happening, even if it's just small things being shared at once, or that they are in the same universe but different timelines would still be neat just to know they're all in there some way or another. If something like that does happen, a lot of people will have some crow to eat lol.