Their "concrete instantiation[s] of a micro virtual machine", their reference implementations, are in Java and Scala, which of course run on managed VMs, which makes me at first glance wonder what they think they've demonstrated with these implementations.
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For those looking for the spec and early impl, see <a href="http://microvm.org" rel="nofollow">http://microvm.org</a>. The paper says it can currently run simple RPython scripts.