I personally would love this but I think that it would be a big risk for the BBC to do and would probably largely only appeal to completists.
The only way I can see it happening would be if they were planning to end the series and move into movies, either with or without Smith. They would be unwilling to use the Movie Doctor for a tv show (why pay to see what you can see on tv for free?) and would want to keep him for the movie. And they'd hardly sign up a new actor for the role for a short tv series to keep the part warm for the Movie Doctor. Certainly if Smith was going to be in the movie, it would make no sense to cast the Twelth Doctor, then return to Eleven for the movies.
If, however, and it's a hell of a big if, they wanted to keep awareness of the character and show up there while the movie was being planned and produced, this would be one way of doing it, without raising continuity issues and dealing with actor egos ('I'm not signing up for one tv series, just so you can use me as a stopgap actor!') or risking the audience like this Doctor better than the Movie Doctor.
But even then, it's still a big gamble for the BBC and, of course, it's dependent on McGann wanting to do it too (though I've a feeling he would).
Personally, if McGann appears in the 50th Anniversary special, I'll be content with that.