Detachers, pylons, rotators and pistons with zero wobble. I.e. if I attach an external fuel tank to a shuttle using detachers or pylons, or a bomb to a detacher, the attachment should be rock solid.

Rotators and pistons should be precisely controllable, to a fraction of a degree.

Pistons need to be attachable at both ends using joints, so that we can use them to raise/lower things like gantries, booms, cannons, landing gear, etc.

A ball-and-socket rotator that can be rotated in two axes -- this would be great for turrets and artillery, among other things.

The speed of rotators and pistons should be programmable using bezier curves. Meaning, the designer has a curve editor where if you drag the control points to make it, say, a bell curve, the rotator/piston's speed of movement follows the bell curve, starting slow, speeding up to the curve's highest point, then slowing down again.