I expect he's saving that card for when and if he really needs to play it.
If he is made to play it, it will likely show the document released last April was a true copy. That will again embarrass the birthers. But then the focus will shift to Hawaii and whether the original paper document can be impeached and whether any shenanigans within the Hawaii government can be proved. Hopefully, the birther circus will fall into final irrelevance next January, when, for reasons having nothing to do with his BC, he returns to Chicago to help his neighbor Bill Ayers ghost-write his memoirs.