I think shorter stays is the way companies are trending, even if it's not the "AM" type of 29er like a Yelli/Nimble9. Just a quick look at the Specialized Stumpjumper and Trek Superfly(both popular XC 29ers) shows that the stays are right around 17.1".

There are a few others similar to the Canfields...Niner ROS9, Transition TransAM, Kona Honzo, Banshee Paradox. Probably a few that I'm missing. And you don't necessarily need to go to something super-short like those bikes -- something right around the 17" mark might be all it takes to make a difference for you.

Yeah, the chainstay length definitely carries over to FS as well. I've owned a few FS29ers and I ended up going back to 26", and in the process of building a 27.5. The FS29er's I have owned were great for covering ground fast, but they all felt stuck to the ground and I really missed the poppy nature of smaller wheels or even the Yelli Screamy. Now for some, that might not be as big of an issue. But for me, at 5'9" and not exactly hitting the weights as often as I should, the 29er FS bikes have some times been unwieldy to maneuver. I guess that sounds kind of contradictory since I do thoroughly enjoy the Yelli('cept that harsh AL frame), but I think that is more based on the geometry and overall lighter weight(compared to FS).