I see two big issues here: 1. "Sane" is highly subjective. There is no single optimal language for all problems and audiences. 2. Pushing a new language to al

I see two big issues here: 1. "Sane" is highly subjective. There is no single optimal language for all problems and audiences. 2. Pushing a new language to all major browsers is hard, like you said. Maybe even impossible, several huge corporations with complex politics are involved. Google is trying this approach with Dart, and I personally don't think it's the panacea, nor do I expect all major browsers to support it. So the only alternative I see is to have a very flexible VM that can run pretty much any language. asm.js proves that JS is actually quite good at that. I'd still prefer something like native client, but asm.js is highly promising: It's downwards compatible and has some potential for optimisation at the same time.