I wonder when the Pluto was created exactly? Had to have been at around when the Netlink adaptor was created, but I can't find a release date for that accessory. SEGA Retro simply lists 199x.
Gotta wonder if it was between the Model 1 and 2, or after the Model 2 (making it a proposed third model?). Also, was this created in North America or Japan? Looks like the first Pluto is owned by an American, got it at a yard sale, and the second is a SEGA employee seemingly living in Japan?
The design is totally boring, but I'd guess it is due to concept purposes. Though it does remind me of a Genesis Model 2 or 3, with the simplistic (almost boring) design.