Has anyone thought about trying this with aluminum? Just thinking out loud for now. Seems that (just a quick calculation here) you could replace the 15 gauge, 1.5 inch, steel tubing with, say, 2 inch, 0.25 inch wall thickness (not sure about gauge value) aluminum tubing and have an even stronger, lighter frame. I haven't verified the above calculations.
I would be concerned with the weight of a steel frame. After all, part of the reason for a lowracer is speed. I have a Sun Easy Racer CX (cro-mo frame) and while it is a stable, fun ride, it is heavy and slow.