The standard RS6 has 560 horsepower making it quite stout. The new RS7 has the same amount but it is likely this "Plus" trim would also be available on the new RS7. Also keep in mind Audi has done an RS6 plus before specifically with the C5 which received roughly a 30 horse bump so the precedent for a sportier and more powerful RS6 by Audi has already been set.
Oh and more power isn't all that is on the agenda. The RS Plus models are supposed to get extra weight savings as well as Quattro division boss Stephan Reil stated, "A Plus model could have more power, or less weight, and a Plus model should always handle differently to the standard car."
Way to step your game up Audi, respect.