WASI is also used as an ABI for ProxyWASM so you can load whatever custom code you want into a proxy to handle request transformations and the likes that are to

WASI is also used as an ABI for ProxyWASM so you can load whatever custom code you want into a proxy to handle request transformations and the likes that are too large or bespoke to fit into plain configuration files. Envoy does this using a C++ host that starts V8, but there are legacy implementations without V8, and alpha implementations that did it with newer WASM runtimes.