Do we need this? Do we "need" anything (other than food, drink, shelter, love...) anyway? In some ways it makes sense, that you remain seated and stable in particular holds great promise. However it becomes rather tricky to keep an ideal, or perhaps optimal (shades of grey there) riding position when the bike keeps adapting around you. There's power output to consider, sure, as well as cadence, weight distribution and areodynamics to consider. To get all of that right on a moving, adjusting frame could prove tricky, especially for the rider who just wants to move forward a bit to stretch. Still, a bike that adapts to you sounds "right" somehow. As long as it doesn't weigh too much, of course.
Darwin Bicycle folds forward for the climbs and sprints