PlayStation VR lets you play anything on PS4 -- even non-VR content -- on a giant, virtual screen using what Sony calls Cinematic mode. As it turns out, this is true of content on systems other than PS4, too.
As first reported on Esuteru (via Reddit) and verified by GameSpot, it's possible to use Cinematic mode in conjunction with things like a PC or Xbox One. The headset plugs into an external Processor Unit, which serves as an HDMI splitter so that your PS4 can output video to the headset and TV simultaneously. However, in place of a PS4, you can plug in something else -- like a PC -- and have that device output video to the headset. We tried it out quickly and were presented with our computer desktop on a big screen. An Xbox One also worked successfully.
How much use this will actually be remains to be seen. We couldn't find a way to recenter the camera, which would normally be done using a controller PS4. As the PS4 isn't actually a part of using Cinematic mode like this, that isn't an option.