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.
This is exactly what I thought they could do, if they wanted to, when Days of Future Past was announced.
But I got a feeling that ain't happening.
The relationship between Marvel and Fox ain't as smooth as their relationship with Sony.