2016 A4 will be made public in September 2015 at Frankfurt Auto show probably. Might go on sale by end of 2015 in Europe, summer of 2016 in US.
A4 is Audi's bread and butter and the current generation is extremely dull and not appealing, and same goes for interior. The New A4 will follow same design clues as you are seeing currently on new A6, A8, or A3. It will be lighter and much economical as far as fuel. Same front grill design and new headlights as in current audi line up. The tail lights will follow the A6 and the interior will be miniature current A6. As far As engines, not confirmed but 1.4-, 1.8- and 2.0-liter TFSI turbo petrol, and 1.6- and 2.0-liter turbo diesels. A 3.0L V6 will also be an option as well. Obviously the more powerful S4 and RS4 will also be available. Hybrid petrol and diesel might also come.