>>Would it be that difficult to fab one of these guys up for even less weight...<<
At a substantial weight savings? Maybe.
I managed to come up with a 2oz version using grosgrain webbing and dual trekking pole back supports (velcro loops sewn to the grosgain), but never quite got it the level of being "marketable." Basically, you can sit in it, but you can't lean back much without the pad (and user) contorting out of place. I suspect this is the standard caveat the lighter you go here, too. A chair kit needs a certain amount of beefiness, and probably fabric sleeves, in order to take the full weight of a reclining occupant.
One UL solution that works well, though... trees. Fold the pad into a chair shape as usual, back portion against any convenient and sturdy trunk. :)