My early thought is that he can be used as a combo guard behind Rondo and Allen next year. While 6-3 1/2 isn't tall, it's also only an 1 1/2 shorter than Ray. And given his wingspan, it may be a wash.
I'm not sure how I feel about a backcourt of the future with him and Rondo given the size and lack of shooting. However, what may happen is that he proves to be a valuable sub for a couple years behind Rondo and Allen, and then when the Big Three leave, he may be trade fodder in the rebuilding effort if he plays well.