English kings were white long before they had an empire, so it is hard to make the claim the monarchy was built on the empire, so that is a false narrative.

While improbable, Prince Harry is still in line to become King. Likewise their child would be in line to inherit the thrown. They would be mixed race, so again improbable but not impossible.

The monarchy is deliberately and intentionally not "progressive" instead as a "figurehead" position it exists to exert a sense of moral clarity without fear of an "election" process biasing their moral compass "right and wrong".

In recent years, I have heard some Americans wish we had a "Constitutional monarchy" to do the same thing believing rightly or wrongly it could pull the country closer together.