I ultimately think the mentality of the Doctor was evolving from Ecclestion up to Capaldi's version. Capaldi's Doctor in my opinion was the culmination of that evolution of self and every Doctor after that now is unique, embracing everything that the Doctor is. There are also 'forgotten' Doctor incarnations to play with should the show choose. If any Doctors returned, I would say it would have to be those in the modern era with the most emotional baggage and time in the universe, even if we saw the resolution of those Doctors. That would be Tenant and Smith.