It is indeed too late for him to contribute this year, but Ian would certainly make for another good frontcourt option next year. If for no other reason than the Spurs do not have another player on the roster, who can block shots, defend and score in the post, other than Duncan.
It's silly having to justify why this guy is worth keeping around. By now, I would hope that Spurs have seen enough to warrant offering him an inexpensive, 2-year contract this summer.
Otherwise, I predict he'll end up in OKC, contributing to an already young, athletic roster that is devoid of a post player, of his ilk.