There is no limit in the database for the number of genres. I think there will be a performance issue though as the album needs to be updated for every track the importer finds. At least it will be limited to 4 genres, but it will still decrease import performance. The importer works by importing one file at a time and only updates the album for the first album track. To handle this it would either need to update the album 4 times or load all album files when creating the album aspect, which of course means more work than currently, which again results in a slower import.Good for me. So max 4 genres for an album.