I also would love the see a D400 but you wonder if it will ever happen. I love my D300 and if wasn't getting it done I might be more impatient. I just don't feel the desire to jump to a D7000 so time will tell.
Nikon need to sort out their quality control issues on the D800 before releasing another camera. I would be interested in a D600 but not if its got AF issues etc