That didn't take very long. Many thanks to MAMEDev, SCSI2SD, and the SCSI CD docs, optical drive emulation is working well enough to mount & verify a Debian install disc on my linux testbed.
This means that virtual disks/discs with sector sizes other than 512 bytes are supported now as well.
I also have a SuperMac SuperView SCSI graphics card on order, which I hope will arrive before things get crazy again at work.
I have assembled one of the first run of boards and it works beautifully, even with my terrible soldering job. I have found an mistake that prevents the OLED display from being mounted on the Teensy side of the board, as the uSD slot overlaps the pins. I suspect anyone who would be using the OLED display would probably have it on cable or would be fine with mounting it over the NCR 5380, so it isn't a huge deal yet.
Many thanks to Hackaday for the writeup: http://hackaday.com/2016/12/25/the-tiny-scsi-emulator/ !
Merry Christmas, Festivus, Yule, Chanukah, Holidays and a New Year!