My question is, what does this have to do with Docker at all? I understand the use case, and I agree it's useful for Docker extensions. But this looks like it has no reason to limit itself to one application; this functionality is useful for a lot of usecases beyond Docker's API, and it could even benefit its design to be a generalist HTTP transform.
Also, this gives me echoes of xkcd [1]. Is the right way to solve the too many standards problem by wrapping it in one more standard?
I also agree that it's a problem rearing its head in the Docker community, but that seems incidental to the problem itself. This is ostensibly fixing a Docker problem, but it could do much more for us all if it didn't artificially constrain itself to that domain. That's all I'm saying.
Still, neat.