The Audi A4/S4 "will" debut on the IAA Frankfurt this September.
And yes the S4 will have the same 354 hp 4.2 V8 FSI engine like the S5 Coupe.
But people who buy a S4 sedan or a S5 Coupe' are totally different.
If you have rugrats you will probably not buy a S5 Coupe' but a S4 sedan or even a S4 Avant will you.

Hans.