What I imagined is that people could load runtimes like node.js as a plugin itself in order to then load plugins written in non-native languages (JavaScript, Lua, etc.; node.js being an extreme example). I wonder if WASM could also be one such "adapter plugin"?

But plugins are still a long way off. Until then, I updated the issue to include your suggestion (thank you for it!): https://github.com/microsoft/edit/issues/17

Yeah the choice usually js or lua. Webassembly is just a new option.