Are you sure? I seem to recall Grammer being cast before Vaughn's departure. And I'm pretty sure that Ratner would be incapable of having an idea that good.
I honestly don't remember. I do recall co-writer Zak Penn saying Vinnie Jones was about one of the only things Vaughn contributed that stayed intact, but who knows.
On the subject of casting, it sounds like Xavier and Magneto in this movie will be much too young for Stewart and McKellen to return, even with digital de-aging. Who could fill those shoes? No easy task, as Tom Hardy might tell you.
I can imagine James Purefoy as Magneto, depending on the era the movie is set. But for Xavier? Nobody springs to mind. Marina Sirtis suggested that James Marsters should have played Shinzon in Nemesis. Might he make a passable young Xavier?
I dunno. Singer did say the film focuses on the "formative years of Xavier & Magneto" but it is possible only a portion of the film relies on Xavier & Magneto as twentysomethings. We did see Stewart as Xavier in X-Men Origins: Wolverine which supposedly will be around the time X-Men: First Class takes place, so it is also possible the younger versions of Xavier & Magneto would only take up a portion of the film, with Stewart & McKellen coming into play somewhat later in the film.