About ending imperial cloning: I don’t think brother Day, or even any Cleonic exponent, can do so.

As Demerzel says, she is loyal to Empire. Right now, that means being loyal to Cleon XVII. Thus she follows his wishes of arranging a marriage and letting him procreate. However, as the memory of Cleon I mentioned to XVI and XVIII back in S02E05, the temperament of XVII had already been accounted for. Therefore I think that when XVII hits 60, the age at which he becomes brother Dusk, Demerzel’s loyalty will automatically shift to XVIII; she is likely programmed to do so.

So all this trying to end genetic cloning is going to result in is demonstrating to Empire that even he cannot end it. And that is exactly what Hari Seldon wanted when he called upon Empire to (try to) end imperial cloning.

This fits in nicely with the overarching theme of psychohistory (and indeed with the theme of Bel Riose in the books): there’s no such thing as a Great Man, no-one is special and outcomes are for the most part fixed and can be known through some fancy math.