Almost did this to mine, but figured away around not doing it.
however, for my bastardized CLK55, I do, indeed have a push button start on it. just got a cheapo momentary push button from AutoZone, found a spot for it in the ash tray and ran 2 wires to the starter solenoid. I had to do this to get around some of the ignition and steering lock components that quit working.
One of my cars has push button and do not like it. Sometimes I push the button to shut it off and it just keeps on idling, have to look at the tach to be sure. With the R170, if the key is in my pocket, it is off and in park.
I made my own "keyless" starter for a previous vehicle. It worked well and was a fun talking point (push button start on a 1989 vintage car).
I'm not sure if I would do it to Baby ('96 230K), as the switches and push button wouldn't look quite right in her interior. Maybe if the ignition barrel ever craps out like it did on the previous car I would look at an alarm with a remote start function (Baby has no alarm currently).