I'm deeply opposed to civ switching. However, I think that Leucarum is right in one point. If civ switching is done right, it could work even for me. The example I think of is Stellaris. You start as a certain race, but as the game progresses you mix and mingle with other races. This can be done up to a point, where your starting race is completely swallowed up by other races or transformed into something entirely different. Sure, your empire still has the same name, but practically everything else CAN change. However, there is still the huge element of choice here, which is an important component if you want to implement something like civ switching or civ evolution.