If I'm a Brit, I would dismantle Constitutional Monarchy after the Queen. No purpose to have it in 21st Century.
It provides a very significant check on the power of the legislature going too far - no, of course, nobody would design this system in the modern day - but it has developed over centuries to create a very stable system of government and simply removing it would create a potential for a Prime Minister to act like a tyrant.
This is one reason why it has persisted - to adequately replace it, you'd need to devise a completely new set of checks and balances, and would you trust current politicians to do that?