A short list of the things wrong with it:
- People vacuum in a back and forth pattern for simple reasons. Rooms are square. Objects in the rooms are square. You don't want to miss spots so you want a regular pattern. You're vacuuming a living room, not driving the Indianapolis Motor Speedway. If you tried to vacuum in grand sweeping curves, you'd just miss all the little corners and wind up with the cord wrapped around the coffee table.
- Dyson mentions that current designs don't work because they have four wheels on two shared fixed axles. Except that this isn't actually true. Look at your vacuum. You probably have four wheels on the bottom. The smaller set of two are probably rotating on fixed axles independent of each other. The other two (the bigger ones that carry most of the weight) are either also mounted on fixed independent axles or are caster wheels like on a shopping cart. No shared axles.
- Why are upright vacuums hard to turn? They're big and heavy. If the upright is completely upright, then the handle probably has a very short torque arm and therefore is difficult to turn.