I still think is faster to send the same message to all than using JSON.parse on each (not to mention much more compatible). Since each worker is going to make a copy anyway (with JSON.parse or by receiving a message), why does it matter?

Also, assuming what you say is true, what's the problem? It's much easier for the JS implementations to synchronize things only with a specific type of typed arrays than sharing all kinds of GC-managed data structures.