Here is a proof of concept on a very fast 4x4 piston door
The door is very simple and moderately compact. It has a T Flip-Flop to stay open and a nice simple design. I'm sure its possible to decrease the size, but I was going for speed. Activating the pressure plate while sprinting and it still opens before you hit the door 3 blocks away. XD
I'm hoping to make more (bigger doors), this mod is awesome guys!