At the end of April, Matthew Vaughn, who stepped down from X-Men 3, wasn't going to direct X-Men: First Class.
On May 4th, he was. What changed?
Mark Millar, Vaughn collaborator on Kick-Ass posted;
The Vaughnster was on the phone last night and laughing about how he was SO CERTAIN he wasn't doing this two days ago, but is now very, very excited. What's great is that they've worked out a way for him to do it exactly the way he wants to and incredibly quickly, the entire turnaround on the project being nine months, Spielberg-style, so he can get it out next June. Totally crazy, but also cool. As I said a month or two ago, the exec who got in touch with me was heading a great team and these guys basically made all Vaughn's fears go away. I really think this is going to be good as it's exactly on his terms.
We're going to meet on Monday and block out the screenplay for the Leinil series you haven't heard about yet. I'm launching the book in September and just finishing issue five of six. Vaughn is writing and producing this picture and still plans to direct, though X-Men obviously now takes precedence. The good news is that this can be turned around very quickly. Strange how fast things happen in films, though. He told them flat out earlier in the week that he couldn't, but they made one crucial change to the schedule that fixed everything for him, though that's probably for he and Fox to tell rather than me.
Mark also clarified;
Fox just came back with an offer (creative not financial) and a business plan that allowed him to do it fast. Things change fast in any business and we all constantly re-work our schedules to fit. Vaughn and I are starting the Leinil screenplay on Monday morning at his London place.
"Leinil" refers to a movie based on the upcoming Marvel creator-owned book by Millar and Leinil Yu.
I dunno, I'd like to think it was a certain Ms Vaughn telling Matthew "I want to play Emma Frost's mum… make it happen!"