> Currently each high level language compiles to its own thing creating huge islands of code. C#, Java, Go, Rust, C etc will all compile their frameworks into the wasm files with very simple facade interfaces.

This is more or less what SmallTalk has been doing for ages. The keyword for that is "image", in particular "single image".

And yes, it poses interoperability problems: http://www.ianbicking.org/where-smalltalk-went-wrong.html