MTS is MIDI tuning standard, for people who want to work with Just Intonation or ‘exotic’ Middle Eastern and Asian scales.
I am one of those people and would love the option to change the tuning table of the A4 (and OT and anything else). This would likely be a global/system-level adjustment rather than a pattern-based one, and there is an existing standard for it as part of the MIDI specification:
https://en.wikipedia.org/wiki/Just_intonation
http://en.wikipedia.org/wiki/MIDI_Tuning_Standard
http://www.midi.org/techspecs/midituning.php
Is anyone else interested in this?