I didn't read the whole thing, but the author briefly mentions VFIO which would have given him access to interrupts so it would have been possible (but for flat-out performance, polling is the only thing fast enough).

I wrote a small NVMe user-space driver using VFIO more than a decade ago this way. Coming from having virtualized ATAPI (SATA) and SCSI, NVMe was such a refreshingly excellent design.