I recall some talk during the lead-up to the Afghan war about the potential for a draft. It wasn't clear at the time just how big that particular conflict would get. It wasn't impossible to imagine it turning into World War-sized scenario against a lot of Islamic countries. The resulting conflicts were small compared to that, but we had to scale up the military substantially and if they'd grown any bigger we'd have had to have a draft.
Now that women are allowed access to combat positions, it's going to be very hard to exempt them from a draft should one be necessary. I can't conceive of the legislature passing any such bill right now (I can't imagine this Congress passing any non-trivial bill, and I don't see that changing), but a wise legislature would want to do that ahead of need rather than after the fact. If women are going to be drafted, you'd need to start registering them now.
I sincerely hope that it's never necessary. And if a war of that scope does happen again, we'll probably be a lot less selective with our weapons of war. (Afghanistan and Iraq were fought house-to-house, because as bizarre as it sounds that was a way of reducing civilian casualties, at least compared to just flattening entire cities as was done in World War II.) So we may well not have a draft even in a bigger conflict. But I think that, while it's politically impossible, a really good pragmatic case could be made for starting to require Selective Service registration for everybody right now.