Several years ago I was given the advice to wait....for the D4. And, I did. And it was worth it by a long ways. Even though some of the cameras have dropped in price, once the new model is available, the used ones will be several hundred less.
As to attending Photokina, well, this is a great idea, but may involve some expense. Not only the cost of the trip but the exacerbation of the acute infection with the NIKON virus which can cause severe purchasing of NIKON equipment......:-)
A word of caution: Jumping into FX is not just about the body. The cost will be felt on each lens purchased. While Nikon has a few FX lenses for less than $500, most are in the $1000 range or much more. So, I would suggest, sit down and decide what lens selection you would like to have in the first "kit" and figure the cost for this coverage in both DX and FX.