For WASM, the performance target isn't Javascript - but native code and NaCl. Considering WASM has had tremendously more time and effort invested into it, and still underperforms NaCl (and JS) signals to me that this is not the right approach.

The WASM runtime ended up from something that ingests pseudo-assembly,validates it and turns it into machine code, into a full-fledged multi-tiered JIT, like what JS has, with crazy engineering complexity per browser, and similar startup performance woes (which was one of the major goals of Nacl/Wasm to alleviate the load time issues with huge applications).