There’s not really anything to replace though, just take away the pomp. You really don’t need to replace that with anything.
Apparently people seem to like the idea of having someone wandering around, kissing babies, sending telegrams to grannies and standing next to foreigners while another terrible brass band marches past. I don’t have a particular objection to that – there’s just not need for people to be born into it, wearing gold hats with diamonds and living in palaces.
Our monarchist friend mentioned Australia. What happens there could easily happen here: on a practical basis the Governor General (chosen by the government of the day, formally appointed d by the Queen) does all hand waving duties. They have no real powers and switch around every few years. People seem to like them. I doubt there is a shortage of volunteers. There is no reason why the same system could not be done in the UK.
Personally, I’ve nothing against the royals as individuals, but their time is well up.
It’s impossible to say anything against the queen personally because she has never said or done anything that is in the slightest bit illustrative of her character or intellect, despite having many opportunities to do so. She is a walking cloud of fog.