Metal Gear creator Hideo Kojima has made comments that allude heavily to Metal Gear Solid 5: The Phantom Pain being a gameplay experience that will extend well beyond consoles. In typical fashion he wasn't terribly specific, but he has in the past hinted at second-screen functionality.
In an interview with IGN Kojima said, "Metal Gear Solid 4 was a turning point: the engine, the multi-platform and online elements. Moving forward I wanted to have a Metal Gear Solid that you could play on whatever you wanted, and that's how we created Peace Walker. Now we're presenting something again that's console-only, but that's not actually true of Metal Gear Solid 5.
"Metal Gear Solid 5 will have many more elements that aren't limited to one console. You'll be able to play the game on whatever you want, whenever you want."
This could refer to many things. Kojima has previously expressed interest in Kinect and SmartGlass for the Xbox One version of the game, which would allow players to create their own mission content and share it.
His comments could refer to something as simple as being able to the PS4 version on the Vita screen via remote play. This seems quite likely, but it probably a tad too conventional to be the only thing Kojima has up his sleeve. Hopefully we'll find out more soon.