> Second, GCed languages need to be willing to fit with the web/WASM GC model

Suppose the Go people make a special version of Go for Wasm. What do you think are the chances of that being supported in 5 years time?

I think it'd be supported by them the moment they ship it. Whether others will be excited to use it is an open question. There's no central registry of "languages supported for WebAssembly", by design; it supports any language that can compile to standards-compliant WebAssembly.