Well, this is supposed to be a prequel to Singer's films, so I have no idea how they are going to do that and still make it work. Besides, even in the original First Class
comic-book, Wolverine was nowhere to be found, so not only does it break film continuity, it breaks comic-book continuity as well.
Supposedly the script is locked, since Singer had developed it with writer Jamie Moss for some time, so Vaughn can head right into pre-production. I would be skeptical, but Vaughn has worked with 20th Century Fox on an X-Men
movie before so he knows the ruthless studio politics that goes on there, since he pulled out before, so I would imagine if he had signed on, realizing the release date and the time schedule, he would be okay with it.
I have total faith in Vaughn as a director after Layer Cake
, so I'm sold.