I hadn't thought about the ratings. I play games to play games, not to get ratings. All the same, the ratings have uses and are something to try to get high in or use to find opponents and tournament brackets. If what I proposed was implemented, the mainstrean variants would certainly still have their ratings. I suppose an overall Chess variant rating could be made up, even as it stands now that could be done. As for each individual type of game picked and kept track of, it'd be an obscure type of rating and I'd leave it in the back pages somewhere until the game created crossed a certain threshold of enough players and games played to make listing a rating meaningful. Kind of like how the provisional rating becomes established for a person, it could be done for each variant selected. As a popular variant got played more, they would join the list of mainstream variants.
Unrated works as you've said. Just being able to try a game out or play an obscure variant would be neat in itself.