Civ switching is something I personally like because of history. However, now that we have a pretty solid post-mortem on 7, we can tell why it didn't work as a mechanic. It interrupts the flow of the game. The game is "one more turn" and everything that happens or changes in the game has to occur seamlessly within a succession of one more turns.
If there is a way to do switching, it's also clear now that it has to be built along with day 1 classic mode where the mechanic can be ignored, meaning the core design of the game can't rely on switching for major mechanics.
Regardless, civ-switching could have been Civ 7's version of Civ 6's unstacked cities. A failed experiment that didn't ruin the one game, but won't be returned to in the future.
There's a weird narrative around Civ 6 that has emerged due to its late-stage success. 6 wasn't hated on launch, and elements of the districts system were praised, but overall the consensus was that the districts was a poor direction for the game to go, and that 6 was destined to be one of the weaker iterations. It just somehow built up a huge audience through some of its DLC additions, and I'm not completely sure what changed. I'm only really conscious of canals being a thing that people love. The other DLC systems seem to be less praised. I suppose loyalty was beloved, and people seem to like how city-states are handled.
So, instead of treating 6 like a one off, the company doubled down on it and its design leadership. That was the mistake.
Again, civ-switching could have been a one time experiment that wouldn't have been as controversial, but with a firm consensus that the mechanic wouldn't continue.