I don't know about the rest of you guys, but I seriously would consider petitioning for Nyko to go ahead and release this to the masses. It was obviously pretty much done, and I know at least for myself, this thing would have been the killer, must-have accessory for the 3DS.
As it is now, what few games for 3DS I want at least use the Circle Pad Pro somehow. And from what I gather, even those games that don't explicitly use it will at least accept input from it; so it's not like it'd ever have to come off. The added battery life and protective shell would only serve to be an improvement.