Myself and a colleague of mine were lucky enough to see part of Audi's developement tech spec for the eagery anticipated RS4.
From what i could gather, the car will use a version of the RS6 engine along with a modified twin clutch system as recently released in the TT. I imagine there will be a manual as well though, but it wasnt shown. Audi are ploughing a lot of money into the development of their paddle shift type gearing system, so i expect that will feature strongly on the new RS4 and all future performance models.
As for body shape. who knows, but an avant would be the traditional and more popular choice.