I think I know why the classic doctors weren't included: Their age.
Well as demonstrated above, they don't record voiceovers till the last minute, and their voices haven't aged quite so much.
We could hear what goes on in his head.
It's a nice idea at least
Green Lantern wrote:
Baker, Davison, and C. baker have aged too much since their last appearance though, especially Colin. He's aged terribly.
We don't know how old his Doctor was at the point of Regeneration. If anything he seemed to have shrunk. We just know he still had curly hair