Amazon has filed an application for a patent which would, if granted and brought to fruition, would allow people to spectate video games with an attached storefront.
The full application, which you can read here and was first picked up by Autconomy, was filed at the end of June in 2015 and published earlier this month. It was only published earlier this month, however, and provides a rough idea of the UI would contain, as well as some of the features.
According to the abstract, the system might also “include user interface elements via which spectators can order, purchase or otherwise obtain demo or full versions of games”. There’s an interesting line as well about being able to “replay previously recorded game sessions”, but that could easily just be a reference to replays already available through in-game clients rather than any additional functionality.
Here’s a flowchart outlining how the storefront would interact over the top of a game, at least in theory: