The Day of the Doctor left him the perfect opening to come back as the Doctor. The Curator (Tom Baker) was more than likely the Doctor much later in his life, rather than the Fourth Doctor. The conversation goes on about the 11th Doctor never forgetting a face, to which the Curator says something like, "I know you don't, but someday you may revisit a few, but just the old favorites" to which their is a wink of sorts.
That is the perfect opening for an actor that played the Doctor to come back later as another incarnation of the Doctor, but with a familiar face. I can see it as an opening for Paul McGann, David Tennant, and Matt Smith to easily get the role of the Doctor back as the 13th plus Doctor. It also allows them to play it different.
For a Matt Smith Doctor, it would actually play out perfectly given the story of him in the universe. He is the Doctor everyone is afraid of. Maybe it wasn't the 11th Doctor they were afraid of, but the 13+ Doctor that had the same face, but because of that, they thought it was the same Doctor all the time. It would also give a possible return of River Song, as she'd never know if was a different Doctor as seen with the 12th and their last night before the Library.
This also works for Paul McGann. He could come back as a 13th plus Doctor, or the 8th Doctor. But if the BBC wants to move forward with McGann as the lead, he would have to be the 13th plus Doctor with the same face as the 8th Doctor.
This works with Tennant as well, though he does have the half-Time Lord handy Doctor to fall back on as well.
Multi-Doctor stories work too. Just the Curator scene allows for the setup of an actor coming back as the Doctor while not being their original incarnation of the Doctor, but a new one instead.