I came across the statement recently that women priests are ontologically impossible. This seems to me an overly strong claim for two reasons, of which the second is more interesting.
First, it does not seem impossible for Christ to have made a co-ed or all-female priesthood. It may be inappropriate, but it seems hardly impossible. It just didn't happen.
Second, suppose that a validly ordained man becomes a woman not through some sort of operation or sex-change, but some truly natural or supernatural process. The identity of the individual would be the same. The priesthood is permanent. It seems then that there would be a woman priest. It doesn't happen, but it isn't impossible.