The rear wheel is the Copenhagen wheel. In essence, it's an electric motor with batteries to fit inside a bicycle wheel as a single contained unit. It harvests brake energy to use later on. Before I discuss the concept, let me get a few things out of the way. It has come to my ear, as a dutchman, that Copenhagen fancies themselves a "world-leading bicycle city"
Of course, this is not true. From the numbers alone, it's easy to see that Copenhagen is nothing special when compared to Amsterdam. 800.000 people live in Amsterdam, and together, they bike 2 million km/day. ( http://en.wikipedia.org/wiki/Cycling_i... yes I'm citing wikipedia, this is not scientific endeavor)
In Copenhagen, they do 1.2 million with 560.000 people. Amsterdam handily beats Copenhagen. And in the Netherlands, Amsterdam isn't even amongst the highest ranking in cycle friendliness. Therefore, when it comes to bikes, don't listen to snooty Danes thinking they're hot shit. They're not. The Dutch are. And don't listen to most Dutch either since they assume they know everything about cycling by virtue of being Dutch.
The other thing I would like to get out of the way is the notion that electrically assisted bikes are in any way excusable for able people. They are not. End of.
From the two points raised above, it is easy to see that the 'Copenhagen wheel' (not for sale in Copenhagen), is a probably not that good, regardless of who is backing it (MIT in case you were wondering). It might be good when viewed within the scope of the design goals and customer demands, but if the demands are misguided and the design goals wrong, you end up with a bad product. However, it looks like the Copenhagen wheel people know nothing about bikes. It's supposedly for city bikes, but the model used to display it is a Cinelli track bike, with all sorts of gizmo's attached to it to make it not spectacularly uncomfortable at slow speeds. This is the automotive equivalent akin to a Se7en with a Chesterfield chair bolted to it. And then fitted with hybrid powertrain. Now, you could say "but this is great for hilly places", and then you realize the Copenhagen wheel website doesn't list the weight of the thing. It's an electric motor with a lot of batteries. A similar system with less power to add electric assist to a bicycle weighs 7kg and that's considered 'ultra light'. So you add at least 7kgs of rotating mass to your bike. Which you have to lug uphill too. Also, you have to interface it with Bluetooth. I've never been able to get Bluetooth working reliably. And even if that works, you have got a touchscreen to control your drivetrain, which you have to manipulate in inner city traffic, while your smartphone is displaying all sorts of 'interesting' data on how much you're not polluting (hint, the same as everybody else on a bike, you're not a special snowflake). For this privilege, you have to pay $600.
As you might have found out, I am quite negative about the Copenhagen wheel. And indeed I feel like a member of the peanut gallery writing this. I usually try to see the good in new products and I'm usually on the enthusiastic side. When Victor Muller took over Saab I was convinced Saab would end well. I am still hopeful that Alfa Romeo will make a successful resurgence and that Lancia will follow after that. Usually, I like new exciting products, even if I have no need for them. However, this Copenhagen wheel makes me weep.