I am all in favour of a Princess inheriting the Crown if she is the older child. This is a very good time to make this change, as it does not affect any current Prince or Princess likely to inherit. We have two generations of male heirs under either system
I am also all in favour of religious toleration, but this issue is much wider than that. It is a big constitutional issue which goes back to the Reformation foundations of the English and then the British state.
We need to hear from the Church of England on the issue of a Catholic monarch, as the Reformation settlement made the King or Queen Head of the Protestant Anglican Church.
Would the government intend to dis-establish the Church? Would a Catholic monarch agree to be Head of the Anglican Church? Would a Catholic monarch appoint another Anglican member of the royal family Head of the Church? What would happen to the style of religious services which the Head of State had to attend?
Would this re-open the Act of Settlement between England and Scotland. How would it affect the Scottish Church? As always, Lib Dems and Labour know they do not like the inherited tradition, but have nothing to offer by way of sensible replacement.