My D400 wish list has only a few things (some of which should have been included in the D300 from the beginning) added to the D300s:
No excuse not to include in a pro DX camera:
1. Pro finder threaded for accessories - that slip-off thing is a real pain.
2. Eyepiece shutter (or AE system immune to viewfinder light). AE in time lapse/remote without duct tape! I have bought three of those little covers. Anybody seen them?
3. Meter mode control with lock.
4. c/s/m mode control lock or AF/MF with AF mode per D800. I admit it. I'm a klutz.
The other things:
5. At least D300 frame rate if the sensor is 24 mp, which I'd prefer.
6. At least D300s frame rate if the sensor is 16 mp. (leaves room for a D400x with 32mp sensor)
7. Really nice ISO 1600, pretty good 3200.
8. WiFi for remote operation, built-in, reasonably-priced compact solidly-mounted accessory or perhaps with GPS in portrait/battery grip.
9. f/8 aperture metering system of the new FX cameras.
10. USB 3 (goes without saying)
11. XQD + SD card slots.
To round out the DX system:
12. DX WIDE LENSES. At least two from this list at intro, 1 a year to follow: 35mm f/1.2, 24mm f/1.4, 18mm or 16mm f/1.8, 12mm f/2.8, 8mm f/4 (or 8-16 zoom), 16mm f/4 PC-E.
13. 50-135mm f/2.8 AF-S VR.
14. 60mm f/1.8 or f/1.4 DX portrait lens.
Would be nice items:
15. Electronic shutter option with EVF overlay in finder.
16. Control illumination (red, please) per D4 would be nice (but I don't expect it).
17. User-interchangeable finder screens with one that provides true DOF view and visual focusing of lenses faster than f/2.8.
And don't mess too much with the basic size/shape/ergonomics. This range of cameras works great in the hand. I think no D4-style joysticks - anybody tried that yet and like it? I'm suspicious.