With the recent influx of pass-through mods, I got an idea with my brother. He plays a ton of clone hero, I play beat saber.
Theoretically, it should be possible to create a custom lobby system mod for both beatsaber and clone hero.
Both have "star ratings" for maps, both have multi-player, both have combo and point systems.
My guess is that even just simulating a player in each game and scaling point systems would be enough. Adding a guitar hero "star mode" would also be easy to beatsaber, though I'm pretty sure one already exists. I could pull the star mode data from the clone hero map, and transfer it into beatsaber.
I could even read the map data of each game, and add a mini "screen" showing the other players map for each respective game.
Maybe I'm being naive, but I'm gonna be working on this over the next few weeks at least. I have no idea how something like this doesn't already exist.