Nope - they still do a 55TFSI S-Line. With 340bhp it's basically an S6 in everything but badge. You just hardly see them as the market is astonishingly small. I understand paradigms point - I'll soon have a 2 mile each way commute and a 540i would be far more suited than my 530d - but people like us are in the minority as most people with low mileage and a desire for a powerful petrol car buy a sports car or something.
The S Series Audi's always were a triumph of marketing - an S4 was no different to a 340i M Sport but because it had S in front of it the market seemed to lose sight of the fact it was roughly the equivalent car in terms of price and performance. This is probably what pushed BMW into the 'M Performance' area.
A 340bhp petrol / diesel isn't really a replacement for the S6. The last version had a 440bhp twin-turbo v8.