I don’t think there’s an equal protection problem if suitability standards are used. Most women don’t qualify for infantry
Sane testing, and the problem resolves itself.
The equal protection issue arises from prior court cases that have tried to force women to register. The argument that prevailed was the women were barred from combat arms, which obviated the need for them to be registered for the draft.
They have removed the reason for the exception, and therefore if they do not remove the exception there is an issue.
Proper testing simply will add to the cost of administering any draft that becomes necessary, at least until the standards are declared to be sexist.