Also, if you haven't checked out PageKite in a while, the most recent 0.5 release fixes a lot of minor issues the older versions had, it may be worth another look, especially if folks are using Windows or aren't based in "the west" (we recently deployed a relay server in Asia, in addition to our American and European relays).
It just happens that the use case for web developers overlaps and that is what folks seem to care about around here. :-)
I don't know how much bigger that is than your vision, since I can only guess what your vision is. :-) I can guess based on your design, that until now you haven't cared much about people using localtunnel for anything except dev testing.
If I were starting from scratch today, I'd base off websockets instead of the HTTP chunked encoding as I did, but other than that I have been very happy with it.