It sounds very expensive to me, think of the engineering required to support the weight of aircraft driving over the top of the terminal, also the safety issues (leaks of fuel, oil, sewage etc.) and the potential for a fire right above the terminal.
It's a novel solution to a problem which I didn't even know existed! But I think it would be cheaper and more aesthetically pleasing if, in stead, the gates were raised creating more of a "drive through" scenario.