This isn't a problem specific to Docker though. If you want to transform any HTTP API composably, you want something like this, and my head is swimming with all of the awesome things you could do with a general proxy that easily allows this.

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.