As an aside, to what degree does WASI exist _now_? The spec seems to be in a state of flux as to what the language the spec is written in is, and the language new proposals are written in seems to have grown futures? On the other hand, as far as I can tell, the latest draft spec doesn't look to have support for UDP or scalable notification (epoll, kqueue, etc.), so is that really what people are using their existing software with?

Docker's great win is that you don't even need to recompile your software to use it, much less port it to what's essentially a new non-POSIX operating system.