I’ve just built up a set of Pacenti TL28s (450g) on Hope Pro 2 Evo 20mm Front and DT 240 Rear Hub with 32 x ACI Alpina Spokes (which weigh about the same as supercomps) and ally nipples. They come in at about 1730g which isn’t too bad for a trail 29er wheelset with a 23mm inner diameter (as per Flows).
However I also recently build up a set of the Light Bicycle 26er Wide Carbon Rims on Dt 240s Hubs (28 x Revs spokes and Brass Nipples) and they came in about 1400g. They made a great wheelset so far, very snappy acceleration and still stiff enough with a the same 23mm inner width for good footprint even from my Mountain Kings.
I would love to build a set up for my 29er (Fireline Evo) but trying to resist as its only my second bike!!. They should come in around the 1500g mark I imagine. Despite my efforts to resist I do also wonder how a 28 spoke build would work out on a 29er wheel. Imagine it’d be ok as many factory wheels use the same and sometimes less spokes with the stiffer carbon rims!
Incidentally the WTB i23 KOM rims have come out recently and they’re about 425g and 23mm inner width again!. (Circa £53 if ya shop around)