Valve has been dipping their toes into distributing non-games on Steam for quite a while. Gabe Newell at LinuxCon 2013 said that they are dissatisfied with families needing to manage multiple content silos, and they would like everything to be accessible everywhere. This can be interpreted as a “situation: there are now 15 competing standards” environment, but it seems to be more in the context of “I have all my content on my PC, why can't I bring it into my own living room?”
We later saw this manifest as Steam In-Home Streaming for PC games. For videos, according to the Streaming Video on Steam FAQ, “In-home streaming is not currently supported”. Still, this seems like it will be their method of getting this content out to arbitrary displays in the future. Also, I have to wonder how Valve's historical practice of distributing purchases made from other stores will play into this whole situation.
For now, Valve has been adding more and more content to their service. It started with a few documentaries and low-budget films, including a video from the publisher of the game Hotline Miami. Now we are seeing the Mad Max franchise including the summer film, Mad Max: Fury Road available on the service. Steam doesn't need to have every movie right now if it wants to survive. They don't have to justify their actions to a board. They do, and they experiment with how it works and why.