@pitch64 "None" or "None Yet"? It's an important distinction.
I just went through the process of replacing my Retropie with Recalbox specifically because I wanted to play Gamecube roms on my Pi4. Recalbox is specifically advertised as being able to run 100+ different systems including Gamecube, though now I see it's not compatible. The page you linked doesn't specify if it WILL eventually be compatible or if it's just not now and not GOING to be.
I would like to know clearly if it's something I can eventually hope for, or if I should just wipe my micro sd and start again fresh with Retropie. If it's just going to be a waiting issue, I can wait. But if there's no plans to make it work, frankly, Retropie already runs all the roms I have/want to play, excluding Gamecube roms. So I'd like a clear answer.