Top items in order of likelihood to turn this announcement sentiment completely around:
1- It has one card slot. I think this matters not at all, but apparently, it's the one critical feature for everyone commenting negatively on the new Nikons.
2- Announcement date: September 18; release date: "first half of 2019," which will mean August 2019 if precedent holds.
3- AF speed isn't as fast.
4- Lag after pressing shutter in most situations, such as current M series. (In my opinion, the biggest real, likely wrench in the works.)
5- Native EF lenses suffer one of several disadvantages, such as lowering the frames per second or preventing metering or AF during burst shooting.
6- Buffer can take 17 images and then craps out.
7- Battery life is between 200-300 shots rather than 700-00 shots (even though it'll turn out that the CIPA standards aren't realistic, and people get 400-500).
8- It takes on SD. Or it takes only CF. Or it takes only CFast. Or it takes a combination of a couple of those. In any configuration 3/4s of people will think it's dumb.
9- It STILL uses the old format of SD, critically strangling data flow for dual card use.
10- Tony Northrup loves it. (Tony, imo, is great, but he rubs this forum the wrong way.)
You can pick 2 from above if you're an optimist, or 3 if you're a pessimist, but hold on, as it's never not happened.