Well, being a contrarian by nature, and having put many thousands of kilometers on the nearly-vintage Kuwahara tandem in the past couple of years, I am coming to the conclusion that the biggest boost to tandem popularity in the past 30 years - namely, the stretched rear compartment pioneered & promoted by US tandem builders - is oversold. Having attended a couple of tandem rallies in the Pac Northwest, it seems to my contrarian eyes that a lot of rear frame space is wasted. The stoker seems to have too much room.
This wouldn't be an issue, except that the longer rear compartment comes at the expense of a longer wheelbase, which I think most would agree is detrimental to "sporty" handling. Maybe this really isn't an issue, as I have heard that Co-Motion has the handling paradox resolved in its frame geometry.
Anyway, just as a mind exercise, I wonder how a "short" tandem would fare? By "short," what if we REALLY shortened the rear compartment, moving the stoker right up behind the driver (much like on a motorcycle). The stoker's stem would be flipped around to the front of the captain's seat post and much longer, so that it would rise up between the captain's legs. The stoker's bars would then be placed in front of the pilot and the stoker would reach around the captain to grab them. The two cranksets might have to be so close together that pedaling would have to be in phase to avoid conflict. If the tandem crashed, the captain would basically be trapped in the stoker's bars! (Or maybe protected by them...). In any event, the wheelbase could be considerably shorter, resulting in faster handling, and the stoker may not feel the bumps as intensely.
I wonder if this has been attempted/mentioned/designed?