It'd be great if we could use itch.io as a way to make in-game stores. Most online stores, both for mobile and PC ask an entrance fee to register a product and take a high % of the money made after that. For first-time indie devs, thats a lot. 

It'd be nice to be able to add new sellable items to a game, and once u buy said item, itch generates an one time usable code, and then through an API, the game could ask itch.io's server for whether or not that code is valid.