I wasn't even thinking in terms of side-to-side balance. With the center of gravity up that high, you'd have to have a long wheelbase or else gentle braking would tend to make the bike do an endo. Likewise, going up a steep climb, the bike would spontaneously tip over backwards. Giving it a longer wheelbase to fix the problem would put you right back where you started wrt having a small footprint, but with the disadvantage of how the stoker is expected to climb up to the 2nd floor seat.