One of Doppio's explicit goals was to leverage existing resources in the browser to bring conventional programming languages to the web on top of JavaScript. Using WebAssembly would prevent Doppio from using the browser's garbage collector; we would have to write our own. It would also prevent Doppio from mapping JVM objects onto JavaScript objects.

The WebAssembly standard is constantly evolving, and now contains some ambiguous statements regarding the ability to take advantage of the browser's GC [0]. Considering WebAssembly's current focus on C/C++ code, I do not believe this will come to fruition anytime soon. If it does, I do not see how it would noticeably improve Doppio's current performance, which is bottlenecked primarily by its interpreter. A contributor is working on a JIT right now to make execution faster [1].

Hope that clarifies!

[0] https://github.com/WebAssembly/design/blob/master/GC.md

[1] https://github.com/plasma-umass/doppio/pull/443