GBSCSI and ZuluSCSI support “initiator mode” that can be used to either image an attached SCSI disk to a file on an SD card or provide live access to it over USB as a mass storage device—with better performance than the old USB 1.1 SCSI adapters too, which top out at about 750KB/sec.
Thanks, looking into this more now.
They are still USB 1.1 however, so they won't be able to surpass that speed limitation over USB.