I'm not sure I expect a "real" JVM to end up back in the browser, but everyone these days does seem to be trying to compile everything else to JS by hook or by crook, so anything that serves as a halfway plausible IR for that is interesting. The LLVM IR, for example, is used more or less because it was the least-bad option, not because it's great for the job (the Emscripten list has a lot of discussion of how not-really-platform-independent it is).