> figure out some kind of adapter interface in order to facilitate swapping between 1.1 and 2 (This can start with a clean HTTP/1.1 interface)

I've been thinking about this a lot with hyper, and I'm about to start work on it (having just finished an alpha implementation of HTTP/1.1). My current plan is to try out a proxy object pattern, but you should feel free to use the hyper code as a leaping-off point for some experiments into how to do the swapping.