That's a good question, and I have no idea--I just came across it because of Termite (which looks quite nice, by the way; those concurrency primitives [which are Erlang's, really] ought to be in Arc, but I digress). My point was really that it is technologically feasible to do so.
ah okay. You are saying it's possible to put this in Arc because it's in Gambit. Okay, sure. Gambit seems to be a much more performant implementation of scheme that Arc is striving to be. I think there is a lot to be said about serializing closures. Persistence is the nasty nasty dark secret of Computer Science. Our only tool that semi works is Relational Databases, but they aren't good for everything.