I'm getting pretty antsy. I love my D7000. It's great for field sports and pretty good for basketball (I can shoot up to about ISO 4000 and be satisfied). The size/weight is right. I like the controls, and 6 FPS is enough for any sport.
But, the AF system in the pro bodies is just better. Sometimes my D7000 frustrates me with slow lock-on, and I'm pretty sure the stronger AF motor in the pro bodies would make my small prime lenses faster for basketball.
I don't think I would upgrade to a new D400 for the AF system alone, but package it with another stop of high ISO performance (i.e. a newer sensor) and more resolution, and I'd be all over it.
But, alas, I'm not sure we're going to see it. I think Nikon is pushing FX down, rather than pushing DX up (like they used to do, when all FX cameras cost $5K+). This way, they can spend their R&D dollars on FX sensors and cater to the pros and the enthusiasts at the same time. To be honest, most D3200 and D5200 users would probably be happy with the technology that's in my old D50. BTW, this seems to be what Canon is doing as well.