Now, we know that Season 7 should start filming Jan/Feb 2012 but it won't be screened until Autumn/Winter 2012 with the likelihood being that a number of episodes will be held over until 2013. If filming for Season 7 finishes around June or July then that will leave Matt with 9 months to a year or so before filming would start on the 50th Anniversary Special - assuming that it will be a "special" as opposed to a full season. He's not going to sit around doing nothing.
There's an interview with Matt in the new "Brilliant Book of Doctor Who 2012". He's asked how he feels about fewer episodes of "Doctor Who" in 2012 and he has this to say:
"Well, I mean, in some respects, for me, it's quite nice. It gives me a sort of mental break from it, and the ability to go and do other things. We're still going to shoot 14 episodes, so there is still a whole series of "Doctor Who" coming, just maybe not all in 2012. And, of course, I get to go into the 50th Anniversary in 2013, which is really cool. That's incredibly exciting. I hope the break next year is a good thing, because it seems that the anticipation is still around for the next series. It's a risk, I guess. But a good one."
No talk of leaving - just talk of a break so that he can go and do other things. I'm not going to read too much into the VH1 interview - and until we get any official confirmation I shall still happily believe that Matt will be the "current" Doctor in the 50th Anniversary Special. At the moment, I have no real reason to believe otherwise.