Looking good! Very good.
I think the one thing that could be a little hurdle is 'space' used as a delimiter. Say that we have "rock pop" instead of "rock, pop" or some other character. How do we know that that refers to two genres, as compared to "classic rock" or "country western" and such, which are clearly referring to one genre?
Also, it seems trivial/obvious enough to use the first word encountered in 'genre' as the directory destination genre, but what happens when we have "rock pop" and "pop rock" (not Pop Rocks!), without a delimiter? (Yeah, I -know- I'm seriously overthinking this, but it's good for my brain.
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Aside from hard-coding every conceivable combination--which defeats the whole point of letting Linux 'decide' and do it automatically--I think going with the first discrete word is probably best, as you've said.