In a recent Steam Beta update, Valve added a few new entries to its EAppType structure. Previously, the options were invalid, game, application, tool, demo, media, DLC, guide, driver, config, shortcut, and "depotonly". The recent update adds five new ones: film, TV series, video, plugin, and music.
These additions could mean that Steam is intending to distribute film, TV, video, plugins, and music; alternatively, it could just allow users to integrate existing catalogs into the same interface. Of course, this is coming from someone with just about zero knowledge of Steam's internal structure. Someone who is more familiar with Steam might be able to say that I am stupid and this specific enum structure is only used the interface with the catalog or the store. I do not know.
What I am confident in saying is that Valve is serious about making Steam a full home theater PC platform. At LinuxCon, prior to the announcement of SteamOS, Gabe Newell discussed the family ownership (and sharing) of music and movie libraries right alongside his discussion of video games. Whether they want to deal with media company relations is a different story, however.
But let's not get too caught up in media for a second. What is a "plugin"?
This entry was what really caught my eye. Could Valve be designing a plugin architecture for the Steam client? Its built in web browser (or third-party browsers if Valve allows)? Or could it be a method of delivering user content for other apps on their system (similar to how DLC has its own type). If it is a Steam Client or SteamOS plugin, what would that even entail? I am definitely curious.