3 pianos 2 hands would be even more interesting
Actually, this isn't that funny. It has been done before. Malcolm Arnold, for example, has a piano concerto for 2 pianos, 3 hands. It is a superb and fun composition. Arthur Bliss also revised his concerto for 2 pianos so that it, too, is for 2 pianos, 3 hands. It was mainly done for a 3 handed duo, one of which had a paralyzed left hand.
It does work. It works much in the same manner a left hand only composition would work (or one hand in general), but just with an extra piano. I've noticed that the person using one hand tends to have the more important part in the 3 handed compositions I have heard. And they really do work, from what I have heard for this combination.