Ditch the touchpad and return to the classic start/select setup. Keep the share button, but make the screenshot/recording functionality much snappier (akin to how it is on Switch). The touchpad, not the light bar is responsible for the extremely poor battery life of the DS4.
Buttons on the back of the controller, SCUF/XB1 Elite/Steam Controller style. Two minimum, four maximum. Make them remappable to any face button.
Interchangeable analog sticks with magnetic caps. Tall or short, concave or convex, textured or smooth. If it's too expensive, release packs so customers can buy the ones they want.
A clickier, XB1-style dpad. If the shape of the pad really matters, keep it, but don't hide the center of the pad so only four directional inputs are visible. Make the whole pad available so rolling motions are more naturally performed. Helps avoid accidental inputs in fighting games, too.