The Queen could have issued LPs (in fact could have done it when she issued the LPs that expanded the HRH titles to all children of Prince William) that would have had the effect of limiting the title of HRH Prince/Princess to children in the direct line of succession, similar to what has been done in Denmark (but before any of the children affected were born). I think it's clear that this was a matter of discussion in the RF for some time and that Charles was wanted to restrict HRH for a slimmed down RF. This was mentioned in media when the announcement was made that Edward and Sophie's children would not use HRH Prince/Princess, and there was further speculation that Andrew was concerned that his daughters might lose their titles. The decision made about Edward and Sophie's children was the first step in the move to restrict titles, but nothing formal has been done to make it official.
I agree that titles should be given equally to males and females. But there's another consideration. Why use dukedoms at all? Maybe there could be a change there. Why isn't HRH Prince/Princess of the United Kingdom sufficient? I understand that it is tradition, but perhaps this could be a change along with some of the others that are being contemplated.
It's been pointed out that one reason for these dukedoms to be granted on marriage is so that the woman marrying in does not have to be Princess Hisname. There is an easy way to fix that as well. Let them be Princess Hername, as the Scandinavian monarchies do. It was reported at the time of William's marriage that that was his preference: no dukedom and Kate would be Princess Catherine.