Upcoming moOde 7 series

[challenge]

that's why I said just add a toggle. it is pretty much unharmful anyway, the comment would only be shown, it would not alter the sorting or cause any harmful issue (maybe UI issues if long characters?)
I know that it's a very specific user case, but plenty of people I know have both vinyl rips and cd or mfsl or HDtracks of the same album. And this feature fixes that issue.

unless of course one decides to ignore MusicBrainz and puts a useful unique text descriptor into the MUSICBRAINZ_ALBUMID field instead of a UUID string.

a big no to that as it would kill the "automation".  
I went as far tp appending the catalog number to the title to dirty fix this, but that's 1) ugly 2) not the right way to do it.
If mpd is trying to follow musicbrainz "standard" by supporting some of its fields, imho it would be detrimental to manually edit those, deviating from the online database. 
Musicbrainz also uses the "catalog number" tag. I like that, as in real life that's what you see on cd's spine. But this can't be used, as it's non standard in the various formats. Not even mpd supports it, while pretty much every format has a comment.

The big advantage of musicbrainz is Picard... you load the folder, cluster it, just pick the correct catalog number (aka release) and it fills/corrects any missing/wrong tags. 95% of time it's perfect with only a few clicks. If it's slightly wrong either you override it, or push an edit to the online database. But long gone are the days of manually writing tags.
You can tell Picard to not overwrite the comment tag, if you're using it for any other purpose. 

In any case, one could append automatically (various sw do this) the catalog number to it, if you have multiple editions of the same medium, or manually at least the kind of medium (vinyl rip etc). I think there's no other way as clean/low effort/"standardish" as this.
If you have a better one please suggest as I need it (without overwriting musicbrainz fields data).