http://en.m.wikipedia.org/wiki/DisplayLink, http://en.m.wikipedia.org/wiki/DisplayPort#USB_Type-C, http://en.m.wikipedia.org/wiki/Mobile_High-Definition_Link. The latter, I think, uses USB connectors but not USB signalling. I also don't know how well OSes support either of these.

It seems video interfacing remains an area of innovation, which means a) getting a new type of connector on every computer you buy, and b) huge confusion in the market for mere mortals (no, I don't know what a HDMI connector looks like, and I don't know either whether it is better or worse than displayport, thunderbolt, etc)

No standard for this use case, so it's going to need a driver of some sort or another. Also, be ready for it to be CPU hungry, as you're going to be without the benefit of any sort of graphics acceleration.