These side-channel attacks are so cool. In 2012, Zhang et al demonstrated a similar cache-based side channel attack across the Xen hypervisor to extract private keys [1]. That is, one virtual machine could extract the keys of a separate virtual machine living on the same hardware.

As cool as these are, most papers indicate the difficulty of pulling these attacks off -- especially given the easier vectors out there.

[1] https://www.cs.unc.edu/~reiter/papers/2012/CCS.pdf