Comment by andyferris

It actually has much the same benefits of Rust removing green threads and replacing them with a generic async runtime.

The point here is that "async stuff is IO stuff is async stuff". So rather than thinking of having pluggable async runtimes (tokio, etc) Zig is going with pluggable IO runtimes (which is kinda the equivalent of "which subset of libc do you want to use?").

But in both moves the idea is to remove the runtime out of the language and into userspace, while still providing a common pluggable interface so everyone shares some common ground.