I can't see how Felton would politely accept a backup role in Boston, given how he poisoned the locker room in Portland this year because he felt Nate McMillan wasn't giving him enough minutes. Questions of ability/talent aside, Felton is not worth the risk to team chemistry.
For the role of backup to Rondo, I think the good soldier Dooling, for all his warts, is a much better fit than Felton.