What's the Point of the Royals in Britain?

But there’s a problem: even assuming political will to do so, what do you replace them with?

I posted the following in one of the threads about Prince William marrying, where someone made a similar suggestion that the monarchy be abolished on Her Majesty’s death:

I wrote that from the perspective of Commonwealth realms like Canada and Australia, which have written constitutions, albeit with large portions of conventions tucked in. I would think it would technically be even more difficult to replace the Crown in the UK Constitution, since it is so amorphous.