You might be enjoying an "electrorheological fluid device" with your PS4. As complicated as that sounds, the concept is fairly simple – it's an material which is thin and flat enough to be rolled or folded, but can become rigid by running a small electrical current through it.
Sony has filed a patent for the technology which it cites could have applications for gaming. Imagine a future iteration of the PSP which could essentially be rolled up like a scroll and put in your pocket, or a controller that has areas which change shape and consistency based on in-game actions.
One potential scenario cited in the application:
"The electrorheological fluid device can be applied to, for example, part of a controller of a home-use game machine as another example of the electronic apparatus of the present invention. A user touches a control section of the controller by fingers, and the feeling of touch is controlled by the electrorheological fluid device. For example, if a game player is defeated in a fighting game, the electrorheological fluid device is controlled to become soft in order to improve the realistic sensations in the game."
Of course, this technology can also be used in a wide range of other devices and has far-reaching implications for portability and "4D" gameplay (in entertainment terms, tactile engagement with the fictional world). The implementation is far off, but it bodes well for exciting new possibilities beyond the traditional controller.
You can check out the patent here .