I finally got around to reading Gilad Bracha et al's paper about Newspeak modules. Newspeak's modularity is based on the idea that the only thing an object can see initially is what is passed in at construction time. There's no global class loader, no global state—so that when you construct an object, you have total control over the universe it lives in.
At first glance, this sounds very different from the way Java views the world. But I think there's a simple way to view Java modularity in terms of Newspeak modularity: just act as if each object's constructor were implicitly passed a reference to its class loader (along with its other arguments). Unless I've missed something, this gives you access to the same universe as the standard Java semantics.
So you could implement a JVM (and a bunch of other stuff, presumably) on top of a system with Newspeak-like modularity, although not the other way around. Doing so might offend the sensibilities of the Newspeakers, but seeing that one thing is a more general case of another always gives me the warm fuzzies.