I believe that we could (easily?) implement transferable strings, just as we have transferable array buffers. This would be quite useful for e.g. I/O: - JSON.stringify data; - send it to worker; - worker encodes it; - worker writes it to disk.
By the way, if someone is willing to mentor me on this, I'm willing to work on it.
Transferable strings imply that the source string would get neutered, which would make JS strings mutable, which isn't going to fly. I think you want bug 852187 instead.
Cc-ing baku at the suggestion of smaug. Just in case either has an idea.