I'll stand up for Her Majesty here. I'm somewhat supportive of Commonwealth countries becoming Republics, but not Britain herself.
I think that those of you who are so quick to throw the monarchy under the bus need to look at the horror that is overtaking American politics in regards to our Presidency. The deep polarization that started in the Nixon era and continues to this day is getting worse by the minute. The rabid vultures on the far-left and far-right demand accountability from their party-mates to their prejudices, fears, and vile hatreds.
Having a non-elected non-political head of state that represents the nation itself would seem like a refreshing change compared to the radical polarization of American political discourse.
(For the record, this doesn't mean that I am not advocating that America have a monarch )
Again, German model.
Among what already exists and what I know that may be my favorite.