There's no question, belt-drive is the killer app for that frame style. I'm just surprised that style is so widely used in the Dahon line, and not just one model for belts; 99% of the ones sold in that style will never see belts, and it's a less efficient design structurally (so heavier) than a triangulated rear, especially in aluminum, to keep those cantilevers from breaking in fatigue (on the bottoms of them, in tension). Now if it could be made of a strong enough steel to let them flex vertically, that's a nice suspension, but even in steel, that's really hard to keep from fatiguing. I do know of a titanium mountain bike with a very simple, low travel rear suspension, the seatstay monostay upper has a short spring of some kind, and the chainstays flex in bending. But if parts for belt-drive and a good internal hub come down in price, there's a plethora of Dahon Mu bikes on the market for conversions. But I still wouldn't put tour weight on it. Dahon is triangulating the front triangles with their Deltec cable design, but that doesn't help the rear.

In recent years I've seen triangulated rear frames with bolt-on dropouts, I think that is the wave of the future; Structurally efficient, belt-capable, and can easily change between vertical and horizontal dropouts if desired, and the same for quick-release and thru-axles.