I've never heard about this powerbox thing, but webpages have worked like this - being able to access only files from a file picker - for decades, so I'm sure that's where they took the idea from.
This isn't really about files, though. Capability UI patterns are about composing all kinds of authority in a usable way. I'm sure we'd all agree that accessing files isn't the best or ultimate description of the interesting things that people do with computers now. This is an area that's waiting to be rediscovered by the rest of the world.