I'm not too concerned about this one. If the ATF does change their mind, I think they'll just get their asses reamed in court and it'll be overturned.
The way I understand it, the GCA of '68 and its revision (FOPA) of '86 are what specifically ban AP rounds (in handguns). Per the law, the definition of AP is:
So, according to the law (which neither the ATF, nor Obama can change by themselves), M855 does not fit their own definition. It's steel-tipped with a predominately lead core.
Its the ATF, once again, attempting to push the limits of their authority. Theyll get smacked in the dick once again and shut up for a little while longer. So essentially, they can fuck off.