It's worth noting, as I've said before, that the hereditary monarchy is simply a convenience. The Act of Settlement 1701 stipulates that the Monarch shall be succeded by their nearest Protestant heir, and that's about it. It's a law which could be repealed today with very little grumbling outside Scotland and Northern Ireland . The Monarch merely exists because the Crown, the institution from which all legal authority in the UK comes, needs a hand (literally) to sign bills into law. Who the hand belongs to the rest of the time is largely irrelevant. By making the post of signatory (Monarch) hereditary, we've been saved the bother of choosing someone for the job every so often and prevented the probem of a power-vacuum when somebody dies.

Given my druthers, I'd hand over Northern Ireland to the RoI, leave the Weslh and Scots to their own devices (very limited without English government money, but they should've thought of that), then chuck the Germans out and find as close a descendant as possible from the Anglo-Saxon line. Also, move the capital back to Winchester and put checkpoints all round the M25 to stop that bloody London lot getting out!