I'd be up for slimming down the Royal Family, and modernising it. As soon as the line of accession changes down a level, then some of the upper levels should vanish. We shouldn't be seeing anything of the rest, at any time, and they shouldn't be there for public events. So for me, it should just now be Charles, Camilla, William, Catherine and their nippers. No need for Edward, Andrew, Anne or any of their descendants to be anywhere near the place, and Harry's largely took that decision on himself, so fair play to him.
Of course, though, they are family, so things like yesterday should be shorter for the public, and give the family more time to do their own thing, out of the public eye. If my grandma died (or great grandma) and I had to go through that all day, before the private part I'd have hated it.
They should have no say in-laws (not that they do much nowadays), and elected MP's/ PM's etc shouldn't have to go to the royal family for box-ticking approval.
I'm not against them living in big houses and having wealth or denying our history (the good bits or bad bits), but their day-to-day living should be provided for by pre-existing legal wealth, the tourism it brings, not the taxpayer, and they should have to pay the same taxes as anyone else, they should end up with less and less over time.
I expect that tourism will drop (after a short boost), as the monarch won't have been there anywhere near as long to build up that constant/ always been there feel, and with that dropping so will support for the monarchy I think. You can see it already, people were all for the queen, without question, but not for Charles, it doesn't make any sense for royalists to think this way (but some do), but makes sense for those who don't care that much, or those outside the UK.
I'd possibly disband the commonwealth, I don't really see the need for it.
I don't think those in line to the throne should be kept out of doing normal "work", they need to see what it's like for the public, otherwise, it's completely unreliable. Doing visits doesn't tick this box, as wherever they go the whole place changes in preparation, all they see is a false version of reality.
We could probably do with putting an age cap on who is king/ queen too, they get looked after so well that they largely live long beyond the average person, and thus become a bit outdated. I'd rather have someone who had spent the majority of their life in more modern times, might make them a little more relatable to younger people.