I think this is the first time I've seen an optical boot configured cube listed on ebay. They are pretty much always upgraded.
https://www.ebay.com/itm/NeXT-Cube-System-Excellent-Cube-Monitor-Printer-Keyboard-Mouse-Cords/253363506777?hash=item3afda44e59:g:bu4AAOSwxOFaWJLQLooks like the original 40mb accelerator drive as well. Not advocating for a purchase, just thought it was interesting.
Good catch! I've had dozens of cubes over the years and never found one with the accelerator drive in it.