accel./rit. in MIDI?

[Mark Polesky]

I know it's not supported presently, but could it ever be
possible for a lilypond file to generate a MIDI file that
speeds up and slows down on command? With commands like 
\accel and \rit that look for the next \tempo, much like 
\< and \> look for the next dynamic. How hard would it be 
to accomplish this from a programming point of view and 
what might it possibly entail? Or is this idea too 
unwieldly to warrant exploring? If such a feature were
feasible, I dare say, it would be awesome.

- Mark