The nice thing about doing a Smalltalk is that there is a colossal amount of software built on top of it. I'd love to know how much of that corpus could operate like this. I don't recall ever using locks, but I also never ran ST on a multicore machine either. It's just that the message-passing idea matches a many-core machine so well it's a shame not to play with it.
Snarkiness aside, that would be interesting. Not just as an educational tool, but it might be useful in the same way as erlang is (large, fault-tolerant, massively parallel systems). But with OOP instead of FP (Elixir attempts to be the "friendly"/more conventional version of erlang, but it is still very much a functional language).