Well. The exchange rate between Euro and dollar really hurts AOA from trying things out often. The certification costs hurt in that regard as well as new models cost money to bring over here. The R63 is a special order model (MB USA only expects 150 per year)

As the RS6 is concerned, 1750 kg IMO is out of reach as Audis are always a bit on the heavy side. But the new Audi S6 handles just as good/better than the M5 (per Car and Driver test [it did have failry poor acceleration]) So the RS6 should handle quite well even if it is a bit heavier. With 580 hp and some weight reduction (1850-1900 kg) it should have very sweet performance.

As for Detroit, I am sure that Audi will have something. Most likely a concept, probably something along the lines of a Q5 teaser. But this leaves the A5 for Geneva (Audi hasn't had any teaser site for the A5 yet).