Doing away with the Linux kernel is a much longer term aspiration. The intention is to use virtualization as a way of reinforcing the app sandbox and/or user profile isolation in the meantime. There has been successful experimentation with this already, but fully integrating it and maintaining it will need to wait until the project has gotten further underway and has more developers that are up to speed on it. It's one thing to simply integrate Xen or KVM for toy examples and quite another to more meaningfully integrate it in an invisible way that preserves the existing functionality rather than being useful only as a proof of concept for research or presentations.