I realize this may not be practical, but it's kind of weird that PCs have been more or less stuck with a protocol designed for XBox 360 controllers for 2 decades now, while the locked-down console space is seeing much more experimentation and innovation around input. The original steam controller at least hinted at being sort of an open platform for this sort of thing, although it didn't really take off. Fingers crossed for the new version.
Back buttons would be another nice one. Right now there's just 2-4 buttons too few on controllers, and it often leads to strange button mappings that either shift with context or require multi-button activations, which gets even more annoying if you have to do it during, say, a jump.
Gyro aiming completely solves both fine aiming and tracking aim on a gamepad when paired with some kind of touch sensitive control for enabling the gyro (natural recentering).
In console FPSes they just automatically track the enemy if they're near your crosshair and call it a day-- giving everyone an aimbot instead of solving the UX issue.