Cap shaft has a hard stop at one end and pushing beyond the limit at the other end may knock the shaft lose from internal plate couplings.
Have you thought about using the changing value of the capacitor as the means to measure its position?
I will pursue the stepper motor + Arduino + rotary encoder with a LCD display idea.
@dc42 - The issue with this particular capacitor is that one end has a hard stop but the other end does not. At the other end, the cap shaft feels as if it has come lose from sort of internal coupling. Not a good feeling and since it is a Russian made capacitor, I don't have a manufacturer who can give me more info about the cap internal mechanics.