Is thing going to be like node.js and allow us to run the Rebol WASM servers with full I/O ?
Non sequitur. Both wasmtime and WASI are unstable prototypes, not "specs", and hence no useful conclusions can or should be reached about them, whether such involve Rebol or not.
A working party is moving towards a spec
Today, we announce the start of a new standardization effort — WASI, the WebAssembly system interface.
And it seems that we should try to have some input into this. And wasn't Carl attempting to do this? Write for an abstracted interface, a machine that didn't exist. Which is what this appears to be what about.