While a neat idea in theory, I don't see how this will work. Chances are that Civ owners who have it on both PC and the Switch will have the expansions for the PC. So how will cross-play from two incompatible builds work?
I do play vanilla on the Switch often and I am hoping the Switch Pro rumors come true as I would like a 2nd setup. Weekends is when I play GS on PC but the Hall of Fame will be fun to update for the standard rules. TBH, I am hoping this also leads to Switch & PC multiplayer. If that happens I will be in heaven. To me, the cross-platform cloud save opens up so much potential beyond the expansions on the Switch.