I was looking through a very old thread about this topic and link that was posted there led to a company making some pretty interesting looking products. This one in particular caught my attention:
This device allows you to use SCSI devices on a USB Mac. The thing that makes it interesting to me, is that the communication must be bi-directional. If the communication is bi-directional, would it be possible to plug this into the external SCSI port on an older Mac via a gender changer and use USB devices??