Subgenre field feature

Not sure if this has already been submitted, but I always found iTunes limited when it came to subgenres or multiple genres. I always had to use iTune's "group" field to enter in subgenres (like labeling The Beatles under "Rock," in the genre field and then using the grouping field to specify other subgenres like "British invasion, rock & roll" etc.). I see that the plans are to bring in all of iTunes fields to Songbird, which would solve my problem of figuring out a new way to sort subgenres, but perhaps addable fields specifically for subgenres would be beneficial, since "grouping" is actually supposed to be used for classical music.