We've all seen the illogic in the continuous "change of mind at baggage claim" of B2-holders/VWP entrants about why they've said they're entering and when they claim they're leaving. If this closes that loophole, outstanding. However, everyone's questions above are well-taken. I think that we ought to hang out on any AILA discussion boards open to us and see what's said there.
What USCIS needs to do is, like Crazy Cat says, to state which visa types are affected, and how, and effective when.
And no one here has yet commented on the extra burden that this will place on the consulates. If they're slow now, look out. And will every consulate have the ability and wherewithal to adjudicate AOS, or just those that currently have decently staffed NIV units?