By 2013, I don't think a Tennant return appearance on
Doctor Who will overshadow Matt Smith. By that time, Smith will be into his fourth year in the role, and the only way Tennant could really overshadow Smith would be if Smith had taken to sleepwalking through the role. I don't find that likely.
A Tennant return would be interesting, for the same reason that Lawrence Miles and Tat Wood in
About Time Volume 3 remark upon Troughton's return in "The Three Doctors" -- being a (or the) junior Doctor in a multi-Doctor story would be something
new for Tennant's interpretation of the role, and something that he couldn't do doing his era. (Though I will admit that the first half of "The Next Doctor" comes close.)
I don't know what I want to see for the anniversary. Someone was talking with me about this in the breakroom at work yesterday. "Colin Baker in a girdle and a wig!" he said. I'm sure a story could be written that brings back everyone from Davison forward, but I don't know that I really want that. Suspension of disbelief can only take us so far, and perhaps that would be a story better suited for a year-long story arc in
Doctor Who Magazine or a beefy hardcover novel from BBC Books.
I almost think I'd rather see something smaller scale. The incumbent Doctor (I'm presuming Smith, based on reports from yesterday's press screening) and a pre-"Unearthly Child" Doctor might be more effective. Perhaps something that ties into the reason the Doctor fled Gallifrey in the first place, it now has resonance in the Doctor's present, and to resolve the issue the current Doctor must go back to where it all began for him.
Alternatively, if the 9/10 console room is still standing (and assuming they have no plans to tear it down), I might commission two standalone specials, one with Eccleston, one with Tennant. Missing adventure kind of things, for the 50th anniversary.
And if Nick Briggs is listening, I'd love an audio dramatization of
The Infinity Doctors, with Paul McGann as the Doctor, for the 50th anniversary.
