Given how unpopular civ switching seems to be (there is a vocal significant crowd outright disliking it and probably a good sized group of people accepting it/coping with it, but few people stating that they explicitly like the design decision the way it was made), I'm surprised that this mod hasn't received more responses / feedback yet:
Preview version of a mod that will allow to play all base* civs on all ages (*excluding DLC at this moment)
In this preview both Antiquity and Exploration civs have been set for testing on all three ages (and all civs are available for a Modern start)
This is experimental, expect issues, and please report them in this thread.
Download here
Installation
extract in your "%LOCALAPPDATA%\Firaxis Games\Sid Meier's Civilization VII\Mods" folder
To uninstall
delete the "classic-civ" folder created on extraction
Configuration
You can edit some parameters...
Me being in the "wouldn't have needed civ switching, but can somehow cope with it..."-tent, I gave said mod now a try...and I have to say, despite this being an alpha version and not able to cure anything, the mod does exactly what its name says and
@Gedemon already crafted a pretty nice classic Civ experience with it. If I imagine that over time more and more civ and leaders will fill out gaps and someone takes up to balance all of them for the concept of "same civ sticks with leader for the entire game", then I wonder if that could be a solution for those just being irritated by Civ-Switching (but e.g. not with separated eras including partial resets)