Well there are a lot of planets like Nekohaven and other planets from rjdunlap, and those planets are hybrids of some vanilla planets, so maybe add your asteroids to em according to their "parent" planets?
https://mods.factorio.com/user/rjdunlap

also paths in mods
https://mods.factorio.com/mod/interstellar-travel
https://mods.factorio.com/mod/AsteroidBelt

Will this ever be added?

I'm very sorry for the late response, I took a break from Factorio modding to work on other shit. From what I remember, the asteroid spawning data for both paths and planets is hardcoded in. So I probably can add asteroids to all of those planets, but I would have to do it manually.