I'm willing to go out on a limb and say the S Class and the Model S aren't in the same category. The E would be closer, but given the mindset behind purchasing each, I'm not certain there is a competitor to the Model S.

There's no equivalent to "buying a Tesla" for another brand, which is a lot of why you buy one. The picture gets more interesting when you look outside the US, where they sell about 15/20% of the E class, BMW 5 series, Audi A4 and other similar cars, which are a much closer match to a Tesla.