"Effects of Extrinsic Rewards on Children's Subsequent Intrinsic Interest" (Green and Lepper, 1974) (
http://www.jstor.org/discover/10.2307/1128110?uid=3737536...) and some other papers which came after it showed that introducing extrinsic rewards to what was before a intrinsically motivated activity could actually hurt long-term motivation.
I wonder if the same would apply here, if this takes off.