> My immediate question which isn't (I think) answered in the repo is how do you interface the NVMe? Can you put NVMe on PCI as opposed to PCIe? How?

PCI to PCIe adapter and then PCIe to M.2: https://www.vogons.org/viewtopic.php?t=78987 (PCIe has some level of backwards compatibility, although like that thread shows there are some limits as to what will work).

This does work on a compaq DS10. You can't boot directly from it but linux will see the nvme disk right away from a livecd.