They must have decided many months earlier that EXPEED6 has sufficient processing speed and power for the D6 ie not spend more on R&D for an 'EXPEED7'
I'm disappointed the D6 is not 30mp, which is far better for many subgenres of wildlife, but the big marketing thrust of the D6 is sports - as we know and Ilkka explains. One hears that 20mp does a good job for the majority of end users. Compared to all the noise in Canon about their Deep Learning AF system, Nikon spells out it out differently from Canon, but it sounds that the 3D tracking etc has been upgraded in the D6.
"With the new AF dedicated engine, the image processing engine EXPEED 6, and the advanced scene recognition system that works with them, the D6 further enhances various performances. In particular, face / upper body detection information, defocus information, and motion detection information improve tracking performance of the subject's movement in the planar direction. " The block diagram under 'Advanced scene recognition system' does not translate from the Japanese, unfortunately and it's not on Nikon USA nor Nikon Europe.
https://www.nikon-image.com/products/slr/lineup/d6/features01.htmlThey also mention AFFT in the D6 is improved for the newer zoom lenses :-) And it the D6 AF should also work a bit better at f8 with a TC
Keeping the ENEL18 and core haptics are big +ves for many of us, and hopefully these stay untampered in an upgraded D850. It could use an extra Fn button and more, however, especially with even more AF modes that some of us may hot-map. Bottom line, I'm another one encouraged that Nikon has released the D780 and now the D6, and let's hope there is a D850 upgrade merging key features of the D6 and also D780 :-) If the AF has top specs, it should meet demands for a '30mp D6'
As the tech details roll out patchily on source webpages (in true Nikon fashion), the sum of the parts will become all the more impressive overall; This is only Day 1 - much more stands to be revealed about the D6 'out there', including where possible comparisons with Canon's new DSLR and its AF.
https://www.digitalcameraworld.com/features/what-is-deep-learning-af-how-does-canons-ai-powered-autofocus-work