Sony has a history of putting little gimmicks in its controllers, and it seems this is going to continue with the next generation of DualSense, as the company has filed for a patent for a controller that has buttons which will get harder or softer, providing more or less resistance depending on elements of a game.
The controller can adapt to gameplay by changing the mechanisms that respond to button presses, according to the patent (caught by Cheat Happens, thanks to Eurogamer for the spot). The controller would make use of a magneto-viscoelastic elastomer. Essentially, this will allow the hardening and softening process to be controlled by the game through magnets inside the controller.
There are concepts for a player being able to push a button and have it then harden around them. The use cases might not be immediately clear to some players, but if you've used the current DualSense for long enough, you'll have noticed how it uses its adaptive triggers and other gimmicky bits to give you that extra sense of immersion. We'd imagine this patent won't be seen in use until we see a new generation of DualSense, but expect the controller to be improved compared to its PS5 predecessor.