My concept for Civ 8 is a "earn keeping your civ alive" premise. The higher the difficulty, the harder it is to NOT civ-switch, and civ-switching will represent a kind of bonus or handicap that makes it easier to recover from being behind.I don't mind all three existing at once! And it's not new to have different stages of a Civ's journey in a single civ. Nobody batted an eyelid at Rome and Spain co-existing for example.
But I really miss being able to take Rome into space for example...
At the same time, you can turn it completely off, and there will be "legacy" civs built out of the most historically appropriate pieces, i.e.: a complete "China" featuring the full Han-Ming-Qinq civics tree. This will be in an included "legacy" mode that ignores civ switching completely. Civs that don't have ancient counter parts will use default trees, or if appropriate, a regionally similar proxy. You ought to also be able to customize this.