It will no longer look like a smaller A8 and/or larger A4.
The current Audi A6 is a fine luxury sedan, a worthy competitor to the BMW 5 Series and Mercedes E-Class. But at the same time it's not much of a standout design wise. Audi wants to correct that with the next generation A6, due to launch sometime in 2017. We're just now beginning to get some details about the next A6, the most specific being it will share some styling elements with the recent Prologue concept unveiled in LA last month.
Audi is promising a greater visual difference between all future models, so the A6 will no longer look like a shrunken A8. In fact, the next-gen A6, A7, and A8 are all being styled alongside one another in order to ensure the designs are not just scaled-up and scaled-down versions of basically the same car. The 2017 A6 (as well as the new A7 and A8) will be built on the same platform as the just launched Q7, therefore expect a weight reduction compared to the existing model. The next A5, essentially a two-door version of the A6, will follow sometime after the sedan's debut.