Technically you don't need a full kernel, edge workers will likely have their own custom trimmed down kernels for running WASM binaries, cutting out a lot of the OS overhead. As long as they implement a limited set of POSIX syscalls they can run WASM binaries, in fact you might even want to limit the WASI syscalls you implement for certain targets.

WASI runners are just an application. I guess you need your kernel to run prograns and have syscalls, but that is a low bar.

Docker needs the 3.10 kernel which is 10 years old.

It also needs root access, and 3.10 is only the lowest supported kernel. Not a docker expert but I could bet that they only support a subset of features there.

What I do know is that docker images are specific to the host architecture, supporting either one architecture, or a blessed list. wasm binaries on the other hand aren't. wasm can theoretically also run on bare-metal embedded scenarios without an OS entirely.

But it needs Linux, while wasm runtimes are available for all OSes natively