IMHO you start at this from the wrong end. The LPs make laws so that an existing situation is adapted to how it should be. Not the other way round. If they dont fit anymore they are changed. So if George would have a girl first, she would be the heiress apparent. Her children of course would be HRH Prince/Princess. There is no way the children of the heiress apparent would be Mr/Miss fathers name while the children of a younger brother of said heiress would be prince/princess. That is simply unthinkable, thus it will not happen, LP or not. The RF may be old-fashioned but not that much!
Indeed. George VI himself issued LPs to make Princess Elizabeth’s children HRH princes/princesses because she was the heiress.
[...]
The British RF , however, seems to be more reactive then proactive and both Charles and William might feel there is no need to deal with that issue until it comes up in a concrete situation.
The opinion I gave earlier in the thread was based on these assumptions:
At the time Elizabeth II issued the 2012 letters patent, she was aware that a new succession law was nearly certain to be put in place (the consensus of the Commonwealth realms was announced in 2011) and that if the Duke of Cambridge had a firstborn daughter (George was not yet born), the daughter would most likely be a future Queen, and would likely have children of her own to follow her on the throne.
There are three possibilities for how Elizabeth would want that situation to be addressed:
1.) She would want the future Queen's children to be Prince/ss.
2.) She would want the future Queen's children
not to be Prince/ss.
3.) She would want the decision to be made when the situation arises, by the future monarch at that time.
As I see it, although I know others disagree:
1.) In the first scenario, the solution most consistent with what she wanted would be to issue letters patent to declare that the children of the eldest child of the eldest child of the Sovereign would have the titular dignity of Prince or Princess.
2.) In the second scenario, the solution most consistent with what she wanted would be to issue letters patent to declare that the children of the eldest son of the Prince of Wales would have the titular dignity of Prince or Princess. This was, in reality, the solution she decided on.
3.) In the third scenario, the solution most consistent with what she wanted would be to issue letters patent to declare that the children of the current Duke and Duchess of Cambridge would have the titular dignity of Prince or Princess. This was the only solution which would have avoided addressing future situations.
I agree that the second scenario would make Queen Elizabeth II even more old-fashioned than her father. But it is difficult for me to understand the point of issuing letters patent of general application, if she was anticipating that they would be applied on just one occasion (before Charles or William adjusted them to the new rules of succession).
It would be akin to her father King George VI hypothetically issuing letters patent declaring that "the children of the eldest daughter of the Sovereign" would enjoy the titular dignity of Prince or Princess, but at the same time anticipating that Elizabeth would revoke them before Anne had children (who would be royal under those hypothetical LPs).
But I accept that, as another poster implied in the Wessex thread, Queen Elizabeth may merely have wanted to emphasize that she was granting the titular dignity to William's children owing to their position as children of an heir apparent of an heir apparent under the then succession law, as opposed to making a personal exception for William's family.