I don't think that drift within music threads about particular musical genres would be a particular problem. "That is, if 8 people want to discuss Gregorian chant, and someone keeps wanting to explain why Appalachian ballads are important, it gets awkward" - I can't see that happening.

Obviously if the talk gets into searching for origins, either of words or styles, it'd likely enough get into discussing roots back in the Old World, in Europe or in Africa. When people are interested in music and in songs, teasing out the sources is interesting. But there's no reqason why that kind of thing should need to divert discussions about the ins and outs of the music, and I don't think it does happen very often.

Surely it's a case where "Build it and they will come" is appropriate.    And here on the Mudcat is a good enough place to start building, I'd have thought. Start the threads and see what happens.