Well Ryde have a 25mm deep alloy climcher disc only rim that weighs 337g. So there is a weight saving for proper disc specific rims. This rim has an internal width of 15mm, can hold 1200N spoke tension and will take tyres inflated to 120 psi. So proven it is it is just no one has done it for carbon yet.
To prove this you really have to show how much weight the brake track would add to the same rim. I realize this isn't really practical, so the real proof probably has to include some math.
We can always find light rim counter examples. E.g. American Classic makes a 300g alloy clincher (with brake track) that is 22mm deep with 18mm internal width ...