I understood all that from your post. I’m just saying that if the distros end up being as inflexible as you’ve described, you may need to look for a way to get flexibility at a different level of the “stack.”
You can add and launch arbitrary non-Steam games from Steam, right? Can you use Steam to launch a script that moves around files in the background and relaunches Steam? And have a named launcher to “switch” to each user?