It totally sounds like the future, but I can't help but hate the fact that it is tied to javascript. React-native with WASM would be a dream come true :)
I personally use scala.js and clojurescript quite a bit, but in every case of an existing non-JS language compiling to JS, there is a semantic mismatch coming from the runtime mismatch. This results from various things like the lack of static types, threads, 64 bit integers, etc. Furthermore, the performance still leaves a lot to be desired.
WASM holds a lot more promise for all of these problems.
I think currently there are more languages compiling to JS then to JVM. :)