This is not a competing standard, it's a complementary, lower-level interface that can be used to implement (and sandbox) the WASI implementation. It's defense-

This is not a competing standard, it's a complementary, lower-level interface that can be used to implement (and sandbox) the WASI implementation. It's defense-in-depth and layering: WASI moves up a layer, and not every engine needs to implement it independently, as it can be a Wasm module that runs on any engine.