Interesting how varied the speculation is on when we'll see a D400. Three months to a year. 'We' obviously have no idea.
I'm also a long time D200 user; from the day it came out. The D7000 is very compelling based on my brief research but I'm in no hurry. No problem waiting another year. If the D400 has features I want and need over the D7000 then I'll get one. If not, I'll get the D7000.
And while it is probably silly for any of us to hold out for a D400 because we've labeled the D7000 as semi-semi-pro and we want a camera labeled as semi-pro, it is likely that the D400 _will_ have features over the D7000 that will justify, for many of us, the additional cost.
I have found the D200 to be amazingly robust and I'm pretty hard on my gear. For that reason alone a full magnesium body will probably keep me waiting on the D400. I have absolutely no objective proof that a full metal body will actually hold up better than a partial metal body or even all polycarbonate. But, if I go with what I know, my D200 has held up well and I'll stick with that formula.
The FX format does not interest me that much even though I have mostly 'full frame' lenses, so the D700 or its successor really aren't on my wish list.