Re: Evan Peters Joins X-Men: DOFP as Quicksilver
As far as I am concerned, "Emma" from XMen Origins was a different mutants than Emma Frost we got in First Class. Same thing with "Shadow Girl" which was supposedly Psylocke in Xmen The Last Stand. They didn't even give her a name. They could easily re-introduce the real psylocke in the future movies. Also Beast looks to appear human again in Days of Future Past, which sorta fixes the small cameo in X1, although it's not that much of a big deal, since it was a 1 second cameo in X1.
The only big issues is the walking Professor X cameo in X-Men Origins, his younger self in X-Men the Last Stand still walking, and that he was paralyzed in the 60s in First Class.