A rather grim discussion for those of us that love David Tennant's Doctor(I am no exception to this. I seem to have strongly implied that DT himself brings out my gay side.) but a discussion that should be interesting anyway. Series 4 is going to be Mr. Tennant's third year, which is usually the last year for an actor to play The Doctor. Yes, the time when one actor explodes and turns into another one.
So what do you think is going to happen to cause him to regenerate?
Whenever I invision the event, I always see him in place of Tom Baker near the end of Logopolis.
An event like this may be possible, because David Tennant has been praised as the best Doctor sense Tom Baker, so they might pull a stunt like that.
But I personally hope it's something much more climactic, something absolutely epic and stunning and incredible that it's going to leave you staring at the screen long after the episode is over. Such a brilliant Doctor and brilliant actor deserves a brilliant ending; but unfortunately it's an ending I can't fathom so far.