[DaveBlake]

Tommy the tags Kodi scans, stores, sorts by, filters, displays, etc. are all hard coded. All but a few are there, but no you can not do what you ask to add any that are not. And no it does not read TIT1, so can not sort on it or anything else.

Zag reading yet another tag is easy, adding it to the sorting, filtering, smart playlist rules, info labels (UI display), JSON API etc. takes a bit more effort. Using the data in relationship to the rest, like the artist roles, more work again.

That tag wiki page is way out of date, almost useless. A fuller ID3 list is TPE1, TPE2, TALB, TIT2,TRCK, TPOS, TYER, TDRC, TDRL, TCON, TMOO OR TXXX:MOOD, COMM, TCMP, USLT, REPLAYGAIN_TRACK_GAIN, REPLAYGAIN_ALBUM_GAIN, REPLAYGAIN_TRACK_PEAK, REPLAYGAIN_ALBUM_PEAK, MUSICBRAINZ ARTIST ID, MUSICBRAINZ ALBUM ARTIST ID, MUSICBRAINZ ALBUM ARTIST, MUSICBRAINZ ALBUM ID, UFID, POPM, APIC, TCOM, TPE3, TEXT, TPE4, TIPL, TMCL

library selection scheme just doesn't cut it for me

With the exception of TIT1, what do you want it to do? Saying "doesn't cut it" really doesn't tell us anything. There is a way to do most things, if you can explain what you actually want the outcome to be.

I can only suggest that you scan your music into a library and see what it can do. Explore smart playlists in particular.