Not in a way that would be useful here, I think: I prefer ~/.firefox/cache to ~/.cache/firefox and this requires the variables being unique per program (although, you could probably wrap each program with a script that sets the relevant environment variables to achieve this effect)

I was thinking along the lines of ~/.data/{prog} without requiring further subdirs. The config, data, and cache would all coexist within the same directory per program

Each of the data, config, and cache envvars would all be set to ~/.data in this setup (though “data” isn’t a name I’d use)