Parking electric powered non polluting trains over diesel powered polluting trains is not my ideal of a breathable friendly solution. With trains routed atop of one another, a mezzanine for passengers will be needed between them. This will place the trains on the top level even higher. It would be far better and probably much cheaper to place these trains side-by-side, with all the trains on the same level. Even in Miami they succeeded doing that.
The fact they have to place the HSR trains over the commuter trains shows they don't really have an alternate site available or usable in downtown Fort Worth. Which brings up the question, do they actually have to place the HSR station in downtown Fort Worth to be economically viable?