It'll be interesting to see how they do that. With the D200, they waited until everbody who was going to buy a D2X right off had done so, then they released the D200 with say 90% of the capability of the D2X.
This time though, they released the D3 and D300 in parallel. Although most of the functionality is the same, I think you could say the apparent capabilities of their new FF sensor (e.g. much better low ISO, dynamic range etc) mean there's a bigger gap between it and the D300 than there was between the D2X and the D200.
I'm not in any rush to replace my D200 with a D300, I'm not a sports photog or whatever, who cares about the new AF system that much. I might be very interested though, if there was a version with the larger, much better sensor that I could actually afford, ie Dx00 priced. So I'm sure they'd sell plenty.