The S4/S5 will no doubt keep six cylinder power but go to a turbocharged variant. The question now is whether the RS4/RS5 will have a twin turbo V6 or V8. One resolution for this is that the RS4/RS5 will follow a similar setup to the Macan Turbo in that they get a larger and more powerful version of the twin turbo V6 motor. Audi could 'borrow' the Porsche design which Porsche developed based on their own 3.6 liter V6 and not the Audi 3.0 TFSI V6. Audi could also ditch the supercharger and simply add turbos to their own 3.0 motor.
Another option is for the RS4/RS5 to get the 4.0 TFSI V8 in order to offer the strongest raw power and torque competition to the M177 4.0 twin turbo V8 in the upcoming W205 C63 AMG.
So what will it be? Honestly, only Audi knows for certain at this point. Car and Driver putting out conflicting reports less than a couple weeks apart from each other shows they are just throwing whatever out there and hoping something sticks. It is really disappointing to see such low level automotive journalism from an established source. Then again, trolling for hits does not seem to be above Car and Driver. They again conveniently omit naming a source.
AudiBoost will let you know more as soon as there is more information on the next generation S4/S5 and RS4/RS5 engines. Count on the reports here to have some actual substance backing them.