The major pain in the arse with wheels at the moment is the need to have a braking surface. It really limits what engineers can do with the surface - things like golf-ball-style dimples (for aerodynamics), curved/angled surfaces, ultra thin walls etc. Get the brake out the way and you can make the wheel substantially stronger (due to the rim shape), pull out loads of weight (due to getting rid of that big thick braking track) and save on machining costs too.
I don't actually think that's the case. It seems that the dimensions you need for rim brakes to function are very close to what you need for structural strength. No doubt there's a bit of weight saving to be had but it's not looking like it'll be really significant.