I've thought the same thing, but I think it will happen after he leaves office. After dismissing those who asserted he was born in Kenya as nut cases and conspiracy theorists all these years, the temptation to rub everybody's noses in it by admitting they were right all along will prove to be irresistible to him. Not only that, instead of realizing that he played them for fools also, his supporters will gloat right along with him.
Wouldn’t that invalidate every executive action he took while in office?
He will either admit that or he will admit he is homosexual.
Heck, he might go for the big 3fer and admit all 3.
Toss in he will admit he is a communist/marxist.