Di2 hasn't been around anything like 20 years. Of course, the new electronic Campy could work with a rocker switch since the main lever is now nothing more than a brake lever.
I really liked the idea of being able to program the levers of the Di2 to work any way you wanted. Since my memory is all fouled up, I programed the levers so that the lower levers went "faster" (right side to smaller cogs and left side to larger ring.) I could have probably gotten used to it the normal way so that I reacted automatically. But reprogramming it took only minutes.