I've barely had time to poke at this much, but it's really neat. I was actually originally going to call "txtorcon" simply "txtor" but figured I'd leave that name in case anyone wrote an actual Tor implementation as a Twisted protocol -- which I guess you've now done :) [...and you're welcome to the name if you want].
Anyway.
For sure "prototyping stuff" was the first thing that sprang to my mind as being useful; I've always had good success using Python to do proof-of-concept things -- and sometimes it's simply fast enough already.
I'd suggest looking at Chutney (a Tor testing framework) with an eye to having your implementation as one option for "a Tor instance" to instantiate. Certainly, if you wanted to go along the protocol-testing/fuzzing lines, that would be a good place to start. https://gitweb.torproject.org/chutney.git/
It would also be beneficial to have some unit-tests.
I'm certainly excited to check it out some more...Thanks for releasing it!
Cheers, meejah