The PA-28 ignition switch does only 3 things. It grounds the P lead of the left mag. It grounds the P lead of the right mag. It closes the circuit to the starter solenoid when turned and pressed in. Failure of the start solenoid quench diode could cause start switch arcing which could perhaps establish a conductive path. My PA-28 ignition switch has, to the best of my knowledge, been in service since 1975 and I have never seen it smoke.
I was once sitting in my MG Midget at a traffic light and saw smoke rising from the steering column. Found out that the turn signal switch had burned between the contacts and was smoldering nicely on the carbonized path when the turn signal was turned off. Easily fixed by cleaning out all the burned material. One of my few "Lucas electric" events.