Fantastic new feature, I wonder if I'm the first ordinary user to be abusing it?
With slightly creative tagging this does a brilliant job of organizing albums that have been released and re-released with different mastering, different media (SACD, blu-ray), quad or 5.1 surround versions, etc.
An unanticipated benefit is organizing this way does an end-run around a longstanding Kodi sorting bug that normally sorts albums like this:
SomeAlbumName (2012 Remix)
SomeAlbumName (SACD 5.1)
SomeAlbumName (Super Deluxe Blu-Ray Version)
SomeAlbumName
<---- last in the list
Disc numbers just need to be jiggered such that each release has a unique number, and you can sort them properly.
This whole thing doesn't work if my tags include proper MUSICBRAINZ_ALBUMID - which I'm happy without, as RELEASEGROUPID, TRACKID and ALBUMARTISTID seem more than sufficient to keep me sorted.
I was tempted to suggest that this is useful enough to warrant making this new feature more generalized, and not quite so specifically aimed at Box Sets per se; but I don't imagine it's a good idea to recommend tweaking and omitting tags as I've done. A nice bit of fun anyway, and since I'm gearing up for a retag of my library anyway I think I'll run with it.