The concept is very interesting. It looks like a good idea for a commuter bike, or even a touring bike. Not having derailleurs to adjust is a novel idea, though after cables quit stretching, derailleur adjustment doesn't occur often. I especially like the idea for a commuter bike as there is no exposed chain meaning you could wear work clothes without getting them greasy. The only problem I see, and where I agree with Baston, is how much would it be to repair if the driveshaft were damaged. It may not be a huge risk, but it is something to consider. I remember a while back that a manufacturer tried a driveshaft design for a DH bike to take out the risk of the chain bouncing off (this was before the advent of chain guides and such).