Well, of course we all have to wait to see what the cameras actually can do.
BUT, an upgrade SHOULD BE AN UPGRADE in better resolution and in clean higher ISO. So I predict the D400 will have 24 megapixels for increased resolution and about one stop higher cleaner ISO. If you feel ISO 800 is "clean" enough on the D7000 I would expect the same level of "clean" in a D400 at ISO 1,600. More resolution and more clean higher ISO should be offered to make the D400 a desirable upgrade from a D7000. Nikon should not use the same sensor as the D7000 with the same abilities and just add better weatherproofing and better video. That won't sell.
Likewise, the D800 should offer visible better resolution (36 megapixels?) and visible cleaner higher ISOs compared to the D700.
And the D4 (18 or 24 megapixels?) should offer the same increase over a D3. After all, these are primarily digital cameras (not video cameras) and each new version must offer clearly visible improvements in digital photo IQ over the model they replace in order to justify purchasing them. Cameras are not like the 50s and 60s Detroit cars where we bought a new one just because it had fins or some other "new" look while still being the same mechanical device underneath that new styling.
All three pro level cameras should be out early next year before the summer Olympics if Nikon can get production up and running (much equipment may need to be replaced due to flood damage and a new Chinese workforce trained or the trained Thai workforce relocated - it must be a nightmare for Nikon managers). While the D4 and D400 will be here by next summer they may first be distributed to pros working the Olympics, then to other pros Nikon has registered and then finally sold to the general public. So it may be about this time next year before you or I can get our hands on one of these models. Sorry.