Raph Koster's A Theory of Fun for Game Design have to do with WildStar? Well, they're both mentioned in the game's latest dev blog. As you may have guessed, it's all about the title's economy, and Senior Systems Designer Charles "Bull" Durham expends quite a bit of virtual ink talking about things like resource sinks, resource fonts, and Carbine's interpretation of "fun" as it relates to resource reallocation.
Durham also mentions item decay in passing, though it's not clear whether or not the game will make use of the mechanic in some form or fashion. "We also want to make sure that when you have to make a choice, it is based on what you, the player, feels is most important. Therefore, the choices cannot be too obvious or too enmeshed in critical needs," he writes. "Item repair, for example, doesn't offer much in the way of choice, so it shouldn't be an impactful, painful thing. We will get into this particular money sink later, but it is a very handy and fair money sink to have."