yindesu summarized it pretty well. Here is some reading material:
- Original Year/Release Date / Mass-tag FLACs - #12 by chaban
- foobar not recognising all id3 (1/2) tags!
- does not recognize ID3 ‘UFID’ tag
- Access to other ID3 Frames
- TXXX:Rating tag in ID3v2
- POPM Support?
- Foobar2000 not showing/supporting synchronized lyrics (ID3v2 SYLT frame)
- Metadata not displaying on specific codec
- [Feature request] Support MusicBrainz ID tag mapping
- Can I make Foobar use ID3v2.4 tags?
- Tags - fb2k versus MP3Tag
- Why can’t foobar2000 see or read
MUSICBRAINZ_TRACKIDtags for MP3s when Mp3tag says they exist? - Taggerscript + Plugin: Separating performers by instrument
- MusicBrainz Tagger | foo_jscript_panel
For the UFID issue try something like $copy(_id3:TXXX:MUSICBRAINZ TRACK ID,musicbrainz_recordingid)
BTW, this has been discussed before in the old thread.
If you still want to petition foobar200 devs they can also be reached on IRC