I'm evaluating the same situation for my D200 upgrade - the D7K came closer to an option than I expected, but still with some reservations. My needs/desires for a next camera would be:
Body: Metal, weather sealed, with grip option Sensor: DX, ~15MP, usable noise/DR/color at ISO6400 Lens Compatability: Ai, non-CPU, etc. AF: Improved tracking and multiple cross-sensors. D300 perf. would be great. Speed: 8fps (at full bit-depth) Ergonomics: Must have AF-On, Bracketing, Mirror-Up, and flash commander. Good use of buttons/dials for shooting options. Features: LiveView and respectable 720p video with AF capability LCD: 3", ~1MPix, good sunlight readability. Articulated? - perhaps. Other: Dual card-slot with fast write capability. Cost: How about $1500... 'ish
Both the D300s and D7K are close and the D400 may exceed these specs. I was assuming a Fall '11 release, but if the D7K sensor is packaged in the D300 body with existing AF, that could come sooner? I'd be happy with a D350!