I understand why many modern monarchs have abdicated. It is a practical solution to the issues of aging & handing on responsibilities to a younger generation when the time is felt to be appropriate. It is in short efficient planning. 45-75 sounds like a very good idea.
However I hope firmly that this practise does not become part of the British monarchy. I attach a sermon from the Bishop of St Albans in which he talks about the importance of the religious service of the coronation. About the monarch being set aside for the rest of their life. About the crucial nature of anointing. About the deep symbolism of the ring.
The British (really English) monarchy is sacerdotal. If the British monarchy becomes one that abdicates then it will have to do away with the coronation service otherwise it would make no sense.
In addition the solemn nature of the ceremonies surrounding the death of the monarch would be replaced with something very different. The spectacle of the demise of the crown in all its awesome majesty would be lost. It is solemn high drama. It quietens a people.
https://www.stalbans.anglican.org/w...ons and speeches/BStAcoronationsermon2013.pdf