Update on the project - I've ridden it in the snow, and didn't think it was miraculous. Anything I was able to ride, I would have been able to ride with the "slim" FS 29er. Deep snow still stopped it, just a little bit later than the slim bike would have been able to do. Rode it on sand, sure, it works, but again, didn't think it was doing anything I couldn't have done on a normal bike, and it felt quite a bit slower even though it's within a quarter pound of the FS 29er.
Today, however, I took it on dry, hard packed singletrack, and had a blast. Might still need to adjust the tire pressures a little bit, it would bounce over roots if I was out of the saddle and didn't account for the root, but it was REALLY fun in the twisty bits, especially when I was fresh and able to really direct it. Seems it responds to a whole bunch of input at the bars, and I easily rolled through sections where I'd normally be considering a quick brake drag to keep my speed under control.
The agressive, out-of-the-saddle approach that really worked for it today has left me thoroughly tired and sore, but it now looks like I won't just put it in the back of the garage for the rest of the year, and that's got me happy.
Of course Tuesday I'm demoing a couple Giant FS bikes, so things might change anyway.