I currently use a D300 and D700, for some assignments switching from one to the other with different lenses attached on a minute-by-minute basis. That means I need cameras that are as similar as possible in feel and user interface, and at least one of them must have good performance at 6400 ISO. Although the D7000 looks like it would match the D700 in that regard, I can't consider it to replace the D300 because it's just too different
But... I'm sure there are other types of D700 owner. Many D700's must have been sold to people who simply want a camera (any camera) that is great at high ISO's, and for them, the D7000 seems to be worth thinking about.
Lastly, there are no doubt those who chose the D700 just because it's FX-format, with no deep analysis as to what they need from it; such people won't have the D7000 in their sights either.