TeaVM[1] has an experimental WebAssembly backend that does something like this. Here's the recent Reddit thread[2].

[1] http://teavm.org/ [2] https://www.reddit.com/r/programming/comments/5899ln/teavm_j...

You just need an AOT compiler that targets wasm directly. AOT compilers already exist for Java and C# for various target architectures; this is just another one.