At Valve's ongoing Steam Dev Days event, it was revealed that an upcoming Steam update will modify Sony's DualShock 4 to map more closely to the Steam controller (via PC Invasion). This will allow more options for players to give their PS4 gamepads a more “tailored just for them” feel.
Lars Doucet, co-speaker for the presentation, basically stated that the Steam controller and PS4 controller have similar API. When you use the PS4 controller through Steam, it then has Steam API and therefore basically is a Steam controller.
"You make the exact same API calls, you only get actions, not inputs, and the Steam API takes care of everything," Doucet said.
Specifically, the update will allow you to remap the DualShock 4's buttons, triggers, and touchpad. Doucet called up a presentation slide showing Doom (circa 2016) using the PS4's touchpad in place of a mouse.
No date was mentioned for the forthcoming update.