I commented on another thread, that I believe a future version of the emterpreter will generate the full JS back from the bytecode, thus eliminating that problem - it will increase the emterpreter size by a few tens of Ks, but that will probably by cached everywhere through CDNs.

And even if it never does - it's politically close to impossible to agree on a universal bytecode, so it is extremely unlikely to happen. (Google already tried with PNaCl - if they can't pull it, I doubt anyone else can)