I get the point a minimal browser and WASM, but Java bytecode ?! Why not Python bytecode ? Seems unreasonable to me to add any specific bytecode support. By layout rules you mean get rid of CSS ? Sounds also unreasonable IMHO.
And no WebAudio and Canvas couldn't be implemented in client WASM without big security implication. If by module you mean inside the browser, them, what is the point of WASM here ?