Most games have a kind of purchase that should be a singleton within a user/character/whatever. A great example of this is the ubiquitous "remove ads" in-app purchase.
Presently, developers have to model this as an item and put logic in to prevent the re-purchase of such items.
I think a very natural extension would be an "on/off" kind of item - one that intrinsically can only be purchased one time for an account. Ideally, metadata about whether or not the current entity owns that enablement would come back as part of the catalog/store metadata so developers can properly and easily mark those items as owned.
Bonus points if bundles which contain only ownership info indicate the owned-status of their contents.
