Why wouldn't WASM implementations do native compilation? It's the norm for most modern language implementations nowadays, anything else would be silly.
I guess theoretically, if we agreed to support the main desktop and mobile/tablet OS’s and chip architectures, and then got everyone to use a standard compiler and IL format (LLVM maybe?) then you might get some of the way, but that would be a lot of work (cool if it happened though...)
The problem right now with warm WASM is lack of features (e.g. you can't do threading), though those are getting sorted.