@Steven,
Understanding that protocols for (mp3) tagging are often unclear and not very uniform between hard- and software, which makes it quite difficult to follow clear regulations, I wonder:
Do you intend to add support for (in my opinion sensible) fields like e.g.:
4.2.1 TLAN [#TLAN Language(s)]
4.2.1 TMED [#TMED Media type]
4.2.1 TOAL [#TOAL Original album/movie/show title]
4.2.1 TOLY [#TOLY Original lyricist(s)/text writer(s)]
4.2.1 TOPE [#TOPE Original artist(s)/performer(s)]
4.2.1 TPE1 [#TPE1 Lead performer(s)/Soloist(s)]
4.2.1 TPE2 [#TPE2 Band/orchestra/accompaniment]
4.2.1 TPE4 [#TPE4 Interpreted, remixed, or otherwise modified by]