It's quite clever in terms of making a relatively short Tandem, although given the frame construction, the stoker would probably be limited to a relatively light weight.
It looks like there is a timing chain on the left side, so that must make for an "interesting" rear hub. It must have some sort of concentric axle system, and to have enough strength to pass the pedal force through the hub, the "real" axle must be substantially bigger than normal, which possibly limits the size of the smallest sprocket (not that I think this bike would need small sprockets for speed), but would also probably require non-standard, much larger dropouts.
Still, an interesting idea, definitely with some value.