"If what you care about is compatibility with Apple/MS browsers, then generate JavaScript from your intermediate bitcode/bytecode"
Which is precisely what the Mozilla Emscripten project does.
Emscripten doesn't treat LLVM bitcode as a first-class target, it treats it as an intermediate target to be translated into JavaScript.
[high level language] -> [low level representation] -> [high level language] -> [low level representation] -> [execution]
This is ridiculous to aim for as your first-order target.
Not really, no. JavaScript is a ridiculously high-level target for another language, and this introduces a huge amount of complexity in any effort to target it efficiently.
You can pare down JavaScript, as Eich seems to be banking on, but what possible technical reason is there for this? If what you care about is compatibility with Apple/MS browsers, then generate JavaScript from your intermediate bitcode/bytecode, and let those browsers be slow and complicated and have worse development tooling.