> Would it be possible to create a farm of Pis, where some objects were on some subset of them, and some objects on another? Even a simplistic example with two Pis, with the object space split between them? Can we use the network to perform language-level message passing?

That's a distributed erlang setup, and I'm rather certain erlang runs on raspi. Pretty sure I even saw Erlang on Xen worked on raspi at one point, so your raspi could be a bare-metal erlang node. Not sure that's maintained / still working though, EoX seems dead.