Yeah, it's everything but a surprise, we all knew David Tennant's going to leave soon, but this whole stuff going on at the BBC is just... rotten.
First the executive producer announces his retirement. Along with his boss, Julie Gardner. And god knows who else. Well, now, for example, the actor in the lead role.
Well, for one thing, it may be a winning strategy after all to completely renew the show with new cast, crew, showrunner, etc, but it's very improbable. Too many changes, as far as I know, Doctor Who's pillar was the fact that even when the Doctor's role was given to another actor, something remained the same, the companion or whatever. But not in this case, since RTD was paying attention to thoroughly erase everything he'd put in the show.
All the characters he created, the companions, and now the Doctor himself.
So, if I think about the show's sake, and just the show, and don't give a damn about the possible personal conflicts or loyalty question or anything that could possibly have been the cause of these reckless events... it's a disaster what's happening there.
It's a bold move not to give the plain viewer anything to hold on to, and they surely won't be reassured by the fact that BBC exec #6469436 says the new Head of Drama Department or who the hell and Steven Moffat are just that damn cool for their jobs.
I was sure that the plan is as follows: RTD does his closure films with individual one-time jokes, like last year's Christmas Special, after eliminating all the recurring characters in the season finale, we would note it's the end of his era, well done. But, since the show must go on, David would be staying for the fifth season, or at least for some episodes in the fifth season, so that he'd connect the two eras, it would be logical, it wouldn't be like a brand new show to start with and assure people that it's still the same show, not a total reboot.
But they did it. I cannot believe, but they did it. David Tennant quit, so there'll be basically nothing in common between the first 4 seasons and the fifth. I don't think that's wise at all. Not even if Davis pens a brand new last-minute companion in one of the films who would witness the regeneration, which I highly doubt he would be planning to do (because, anyways, now is too late to make the viewers accept and befriend a new companion).

Also, I left my main argument to the end: the one about the plot, the most important thing of all.
Isn't it like genuinely screwed that RTD said goodbye by a season finale where -besides sinking down to the level of a fangirl- he inserted a cop-out regeneration, enraging many fans, and now immediately after the fake regeneration there comes a real one?? It's like stupid. The cop-out regeneration was the number one reason why I thought Tennant would certainly stay for another season, because I thought, honestly there would be no writer crazy enough to write him out of the show after using the same plot device for a cheap cliffhanger.

So, either the whole BBC are outta their minds, or there's something rotten in Cardiff.
I just hope Moffat can cope with the situation and eventually save the show from disaster.