This is cool. It looks very simple and if you make new door panels, I'm planning on aluminum, you can eliminate the hole and install flush mounted switches.
The limit switches probably protect the motor and the regulator gear from unessesary stress. Most power windows seem to go up (or down), bottom out and flex the door a little, then shut off.
Now...can you figure out how to make power rear windows??? Some minivans have them. I've seen the motors, remotely located above the headliner, drive a cable that moves the window linkage.
Those back windows are now almost impossible to open with a full cage.