https://blueprints.launchpad.net/nova/+spec/encrypt-ephemeral-storage
There is a patch for this upstream, under review, but waiting for reviewers. https://review.openstack.org/#/c/40467/ Last patch set Aug 13. I will review it and hope that helps move it along.
Still under review, and failing tests.
I don't think we have a need to track this specific RFE. This was from when we were trying to track *all* blueprints.