This is about the coolest prototype thing we've ever seen: not only is it an unreleased prototype controller, it's a controller for a system that never existed. This controller was a prototype for the development kit of the Nintendo/Sony SNES CD system.
You can see in this early prototype the beginning of what would become the PlayStation controller: the triangle-shaped start button and the eight gameplay buttons (two of the face buttons would become shoulder buttons in the final controller). This thing would be the prize of any game collection. We don't know how this eBay seller got his hands on this thing; we'd expect it to be locked up in Nintendo headquarters somewhere. It must have been an ordeal to obtain.