So Catholics are still debarred from holding the throne of England. Big deal.
If this restriction were removed, it could only be because the Church of England ceased to be the established church, or the monarch ceased to be the head of the Church of England. I don't think either of those would be good things. I think it is good that England retains an established church, one of its very few vestiges of a great historical Christian civilization. And I am a monarchist to the marrow.
Yes, the English Reformation was a disaster. But it is better that England retains an established Christian church than otherwise. Perhaps it makes little practical difference, but it is at least a link with the nation's past.
Nobody would really care if a nominal Christian of whatever denomination ascended the throne. However, plenty of people would be upset if a convinced Christian of any denomination became King or Queen. (Of course, Queen Elizabeth II is just such a convinced Christian. I am talking about the future.)
I think Catholics would be wrong to make an issue of this. Why ally with the forces of "anti-discrimination", in the crude way that idea is currently construed? The eligibility of Catholics to the English throne would not come about through religious tolerance, but religious indifference. And that's not the right way for it to happen.