I can't see St Paul's for Harry and Meghan. Too vast, too expensive. I can remember that, even at the time of Charles's wedding, questions were raised about the venue and cost, and that was a State Wedding of a POW!
I can however see the Abbey, religious questions aside. Divorcees can now marry within the Church of England if the vicar of the parish concerned is amenable. I believe Harry, as a senior and very popular Royal will marry in London in order that the crowds can see them, or Windsor, same thing, and there will probably be a balcony appearance at BP.
I'm not so sure that Eugenie, who is a very modern princess, will be marrying within the next couple of years or that she will wed in St George's. I can see Eugenie and Jack going for something completely different perhaps, and Sarah backing their ideas up, though Andrew might wish for a traditional wedding. I'm not so sure the York princesses' weddings will be televised either. They are not very popular with the British public, unfortunately.