Currently there are several WASI proposals that are being developed. The State of WebAssembly survey provides a comprehensive overview of the existing WASI proposals and which ones the community are most interested in. There is a lot of interest in I/O, sockets, filesystem, and threads. The Enarx project in particular is investing in advancing WASI support in the Rust language, and we have contributed upstream to sockets, threads, and crypto.
Source: Enarx's Blog