One thing I do like about the F6 (I don't have it) is I-TTL flash. Having said that, I am still very pleased with the TTL of the F100 and my SB28 speedlights.
Cameras, especially the F bodies got bigger and bigger culminating with the F5 then the F6 was released and it was similar in size to the F100, no integral vertical grip. I remember a few posts questioning if the F6 was really an F (I think it is).
If Nikon were going to improve the F6, I'd like to see an F7 with current metering (3D Color Matrix II), AF (51-point), 100% viewfinder, perhaps interchangeable viewfinders, interchangeable focus screens, I-TTL flash...everything else could stay the same.