Lots of good points here.
I don't think that Matilda is actually recognised as being on the monarch's list of England but I understand where you're coming from.
I think the best option would be to have the inheritance system changed so that if the only surviving family member is a princess, she immediately marries and her husband becomes the new monarch.
Do you think this would be easy to implement?

Whilst they do this, they could also add back in the option to choose your heir. It constantly bugs me that my 24 year-old King has a 28 year-old adopted heir because no-one is havng babies.