Unless they want to go ahead and break compatibility, finish going to string-based instead of integer-based, and force everyone to do a new world.
Yes, it would be a bad idea to do so, but that doesn't mean it couldn't happen. I remember all the drama in Beta 1.7 when they changed WorldGen to get rid of the Far Lands glitch and do a few other things in the process. Yes, it would be drama with whining and complaining, but it would be over and done with. For an end to ID Conflicts? I'd be willing to put up with mandatory world resets.