It looks like the bustle back trunk lid (a.k.a. "The Bangle Butt") is being given the heave-ho, although the convertible that was spotted looks like it might be sporting a two-piece rear lid similar to the 5 Series Gran Turismo. It also appears as though there are two cut-lines, the lower one being the one that goes along the side to open for the top to go up and down. The second smaller one higher up might be just for cargo access.
Another element that some will be to see go are the flying buttresses on the top. Thankfully, it appears that BMW has decided to avoid the unnaturally long rear deck that would come with a hard top and retained the fabric variety. At the front, the 6 gets a more vertical grille and headlights that look much like the Z4.
Underhood, the current 4.8-liter V8 will probably be replaced by the newer 4.4-liter twin-turbo and the six-cylinder will probably be the new 300-horsepower single turbo unit just announced for the 5 Series.