I suppose they could make it a "conscience matter" at first, then look the other way as more and more JWs celebrated. But it's a sticky issue for them, because for so long it was one of the ways they differentiated themselves from "false religion" and "Christendom." If they end up saying it's okay, then decades of denounciation go out the window. Also, one of their rationales was that Xmas has pagan origins, and that's not entirely false.
On the other hand, if you're going to say it's okay to celebrate Jesus's birthday, then birthday celebrations are also okay. Next thing you know, Easter is on the table.
Honestly... I just don't see it. It would be a clear sign that they are going mainstream, and the whole idea was that mainstream Christianity is a tool of the Devil designed to draw people away from Jehovah. From Rutherford's time, they did not pass up a chance to attack non-JW denominations as false, as offensive to God. That is a whole lot of history to turn their backs on. How many books/magazines would they need to destroy to clean up that mess?