That being said, at first glance it doesn't look like Clio is using this, instead it's passing messages as you suggest. It might actually be interesting to use SharedArrayBuffers as a compilation target, as they're probably hard to use correctly manually. That being said, WebAssembly threads (https://github.com/WebAssembly/threads) may be more appropriate for this.
For completeness, Workers can also transfer memory (https://developer.mozilla.org/en-US/docs/Web/API/Transferabl...) with less security restrictions. They can also collaborate by accessing a shared database (https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_A...) though this is obviously slower than shared memory.
In general I have to agree that WASM needs more time. There are multiple quite crucial proposals in the pipeline (reference types, interface types, threads, tail calls and other advanced control flow, module linking, (GC), ...) which have all seen very slow progress.
Overall I'm still bullish on the potential of WASM for universal deployment, but the slow pace is a bit concerning.
There are so many parties interested in wasm, there are a ton of inflight proposals and extensions to get it beyond the mvp stage.
[0]: https://github.com/WebAssembly/threads [1]: https://github.com/WebAssembly/multi-memory
0 - https://github.com/WebAssembly/proposals 1 - https://github.com/WebAssembly/threads
Not to forget wasm is in very early stage, once we get threading support(https://github.com/WebAssembly/threads) we can get much better results.