I suspect that a slimmed down monarchy will be the worst of both worlds for royal support. Charles planned that in another era.
People don't want money wasted, but we are much less sensitive to inequality and flaunting of wealth than we were in the 1990s. And so much of RF wealth is buried in estates and funds etc that it doesn't seem to bother people.
People do want glamour and nostalgia. QEII had a rough period between her glamourous youth and her years as the nation's granny. The RF wasn't all dull duty before the days of Meghan and Harry. People enjoyed (let's face it) the antics of Margaret, Diana, Fergie, the young princes. It's all a bit sanitized now.
I suspect Charles would be better off getting the two York princesses on board if they were willing, and Edward's kids eventually too. More appearances from Anne's kids and grandkids too.
The Yorks might cause a bit of an uproar. It would probably do no harm at all in the long run. No working Royals under 40 - and most over 70 - is no way to run a show. The Wales kids appearances are limited - good for the children I am sure - and intensely curated. So other young blood is needed.
I'm not a monarchist, so I don't mind what he does. But I suspect slimming down the monarchy - unless the plan is to follow through by slimming down its role - will backfire.