Just a quick note:

Yes, there is a snippet of the Ninth/Tenth Doctors’ coral TARDIS theme and console in the trailer for Series 6.

However, the guy on the right is NOT David Tennant, it’s Rory (with Amy). You can tell by his facial structure and clothes (and her flaming red hair).

Although I have absolutely no bloody idea HOW that TARDIS theme is going to come back, and how the companions, and perhaps the Doctor end up in there—no, I don’t think either David Tennant or Christopher Eccleston will be back. AND IT’S BETTER THAT WAY. Rory, Amy, and Eleven might end up in the old TARDIS while whatever Doctor’s responsible for it at the time is out, saving the universe. And perhaps he wouldn’t even notice they were there–no damage done, probably, and the TARDIS doesn’t always tell him everything, which could be why Eleven doesn’t know this is going to happen; and we certainly don’t know, because this is one of “the bits in between.”

The strands of golden light might be regeneration energy, they might be a force field, they might be strands of the Time Vortex… could be many things. And I think that that’s a Dalek right slap-bang in the middle of it, but I can’t be sure.