Well Smiths the main doctor now, so he'll be in it for sure. Ok, if you don't think Pual and David will return, who else is there? Ecclesten will not return, that's fairly odvious (there may be hope, but I highly doubt it). Mcoy could come back. Apart from that, it's only Pual and David who have not aged to badly. They may add davidson, I hope against it and doubt it though.
Also, I have a feeling John Barrowman will return, he may not, but seeing he's become a big part of the modern doctor who mythos, I think he'll return.