Having two sets of tubes or structural elements like that, increases the frame "depth of section" in longitudinal bending, and this being a cube (x^3) relationship I think, means a little increase goes a long way, so should give the frame great strength for better fatigue life in the long term, and also reduce stress on the hinge.

I achieved essentially the same thing but reversed, with a typical (high-position) monotube (Dahon Speed), and then adding a tension cable underneath (a la Dahon Deltech feature on their newer frames), which can be very slender as it is in tension and not compression. This provides a full "main triangle", so now the hinge is loaded mostly in compression and not bending. The cable or line simply bends easily when folded. Dahon is slow in making available an aftermarket version of Deltech so I improvised one from kevlar line, can also use UHMWPE (AmSteel, Dyneema, et al) as all are high strength and very low stretch.