Professor River Song
...If he did show up as the Meddling Monk, however, they would really need to explain what really happened in the Time War for not only the Doctor and the Master to have survived, but also the Meddling Monk. I wouldn't be surprised if Romana eventually shows up from E-space, but they should at least tell us the real story if the Doctor's been going around stating that he's the last Time Lord and there winds up being more and more that end up making appearances.
Return of Romana. Hmm. I could definitely watch that!
