Well there was an evil Doctor created as a result of the 13th regeneration.
Didnt they say he ( The Valyard ) was from somewhere between his twelfth and final incarnation
I too think it was implied that River killed the Doc sometime in the future but i just think its too obvious really.
Now my theroy is we keep seeing a future 11th Doc popping back, what for i dont know. Remember in the 1st episode the shadow running past the window well i think its the dr from the future coming back for some reason, landing the tardis silently like river showed him.
In Episode 2, amy had recorded the message saying get the docotr off the ship, this wasnt really explained.
In the last episode, after the angels had taken the doctors jacket, he mysteriously had it back on when he was telling amy to remember what he told her when she was 7. And it was a darker colour.
Dunno, but im enjoying it so far.
I think Matt is brilliant as the doctor, ive taken to him much more quickly than i di to tennant. I also think that amy is brilliant as well.