Things have changed since the days of Old Who, when the handover would be fixed up and completed in weeks or at most a few months; now we have over a year to go before we see the last of Ten.
I'm not going to get into the guessing game of who Eleven will be. Speculation at this stage is rather premature. Anyway there is the old saying that he who goes into the conclave as the next pope comes out of it just another cardinal. (Though the old saying is sometimes wrong.) I imagine the Moff will have someone in mind, and probably it will be someone he has worked with before; one could easily draw up a likely shortlist after a brief session with IMDB, but I'm not going to bother.
Instead I will note that some of the greatest Old Who stories emerged from the creative tension of the great changeover of 1974, when producer, script editor and Doctor all changed roughly simultaneously, and most particularly when the new script editor had been responsible for some of the better stories of recent years at the time. So I have high hopes for 2010.