Yea, if it was during Smith's first year, I could see Tennant worrying it might step on his (Smith's) toes, but, since it will be into Smith's 4th Series, I can't imagine Tennant wanting to miss out.would tennant reprise his role again?.
When Tennant left he said he's looking forward to returning for the 50th anniversary. And he is enough of a Doctor Who fanboy that I don't see why he would turn it down.