Of course it can be done. That's how they fabricated the prototypes. But can it be done as a high-volume low-cost automated mass-production process? How does this compare in cost and speed with traditional automotive body fabrication?I have worked in the Aero space industry building satellites and aircraft for almost 40 years. Manufacturing SS into boxes ore other shapes is not much different that aluminum. The 3mm thickness just changes the bend allowance. It can be done with scoring and hydraulic bending breaks it is all just metal. Manufacturing in SS is not as easy as aluminum but it is the same process. Plasma cut pieces with linier bends, as we see in the CT make it straight forward. The attach flanges of the panels that will be welded or attached to the frame to form the exoskeleton will not be that complex. It is the simplicity of the CT that allows this method of construction.
I hope that you are right and that in the coming months we will begin to see videos of trial runs of this process at Giga-Texas producing test exoskeletons stacked up inside the plant - as we did with the giga-castings for the Model Y.