Why would we possibly return to a manual memory management, raw pointer oriented, assembly language level of abstraction from the much richer and safer abstraction that JS already has? Wasm doesn't even have any notion of Characters or Strings! You really want to return to the days of each project having their own String libraries, because it's all built on top of raw asm?
Webasm is not for JS-style code! You can't have "a little pre-compilation of JS to WebASM", that makes zero sense. We already have the incredibly complex JIT compilation of JS to x64/ARM/etc, which necessarily interacts with the garbage collector, type system, permissions & security, browser debugging/profiling tools, etc, all of which wasm does not have any notion.
Wasm is a raw C-ish sandbox environment for cross-compilation of static languages to expose their behavior to javascript, for straight-line CPU performance in number crunching as in games, software rendering, numerical analysis, compression/decompression, etc.
Just wait until the JVM and Flash Runtime are ported to wasm. Downloaded and compiled on every page load :).
Why that, instead of caching common components like any other web asset, or even having the browser act as a dependency manager?
There are bound to better solutions than "download and compile on every page load."
If C++-to-WASM via clang catches on, I think this is exactly what will happen.