I certainly wouldn't want to limit what's possible to what Java or Javascript are capable of. Certainly not Java. Java is (IMO) practically defined by stagnation as a result of poor management by the companies that have owned it.

And part of what I'm thinking here is getting away from the limitations imposed by Javascript. For example, Javascript lacks big integers, and is a dynamic language. My thought is that decoupling the HLL from the runtime would allow for faster evolution, because it's hypothetically easier to add new opcodes to a bytecode and VM than it is to make large shifts to a high-level language. Consider the whole dynamic thing in particular - .NET has a great VM with pretty good support for both static and dynamic languages. Java didn't, but again we aren't strictly required to repeat the mistakes of the past. And by just using "Javascript as the bytecode" we commit the reverse sin - that's a 'bytecode' with poor support for static languages.