I don't understand why Nikon would produce an FX version of the D90? Outside of these forums, is anyone really interested in such a beast? If you can afford FX lenses and have the biceps to carry them, then the D700 \ D3s \ D3x are absolute no brainers. What is in it for Nikon to produce a lower cost, lower quality version of any of these cameras? I really don't think (from a business perspective) that it would gain Nikon anything - it would potentially canibalise D700 sales without increasing revenue. I'm happy to be wrong ... it is an occupational hazard of trying to predict what Nikon will do next .. but I just don't see the business sense in it. Ok .. that means it will happen tomorrow ;-)
If the camera 2 rumour from the blog comes to market as DX - 16 MP, with ISO quality near that of the D700 along with HD video then that is one killer camera for the vast majority of the market who shoot for fun, print few and only relatively small photographs and put most of their work on the web. In fact, it is crazy overkill for such requirements. But at least sensibly priced crazy overkill.
So by all means shoot FX and no doubt get moderately better image quality (though not necessarily better photographs) for a huge extra expense. I can understand that Pros need it .. but then they are well catered for already - the only real complaint I hear on this forum is that Nikon haven't released enough new FX cameras, not that the quality of the existing ones are bad. But some of us want a good DX camera that doesn't break the bank. An upgraded DX based, D90 would fit the bill very well thank you.
Have fun ... it will certainly be interesting to see what Nikon have to offer.