MIDI from a DI (Live)

ReaTune, just tick the midi output box somewhere and it will send midi info to your track.

Bear in mind, it sucks. It's just a fun tool at best. Can be used for creative experiment maybe, but that's about it

There are some piezzo/DI/whatever sensors you put on your guitar which work just like pickups except they send DI info, but I have no idea how acurate these sound.
 
I'm not sure there is a practical way to do this live without latency or inaccurate midi being sent. So for fast, unlatent midi reproduction you would probably sacrifice accuracy to the original sound source.Unless you hire a keyboardist instead playing the same thing as the di haha. I Hope I'm wrong though cause it would be fun to try.