After the upcoming announcement on September 15th, Nikon may have another announcement on September 20th, one day before the start of Photokina. Back in 2008, Nikon announced the new 50mm 1.4 lens the day before the start of Photokina. If true, the potential candidates for this third announcement are the new Nikon EVIL system or a new full frame DSLR camera (this is not a rumor, just my humble opinion).
I do not have a good feeling about this third potential announcement, [NR] probability rating is "only" 40%.
FYI: today Nikon started a new "I am Photokina" website: