The core of the issue is that the potential IQ improvements of FX over DX seem to be narrowing. That will make FX more of a niche format than it is now, but I don't see FX going away any time soon.
The sensor improvements of the D7k raise another interesting possibility, which is that the next generation of FX cameras may provide DX performance that really rocks, making it more attractive for users to use DX lenses and to use DX mode with their long lenses. Today, many shooters have an FX body that they use to get the ultimate performance when needed and a DX body to take advantage of the crop factor. If one body could serve both needs, so much the better. Put it this way: if the 10 MP DX image of the D3X came with the same high-ISO performance as the D7k appears to have, the D3X would be an even more versatile body.