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. He could also be referring to the Vita's remote play with the PS4, which all sounds really interesting.