Don't see a 9800gtx/s coming out by the end of the year unless ATI ups the anti with a card that can actually compete with nVidia's 8800 series. And have they given any indication they plan to do this? If they've got something waiting in the wings, the holidays would be a good time to release it into the world.
But even if this happened, would nVidia have enough motivation to come out with the 9800s so soon? If ATI's offering turned out to merely match (or barely exceed) the 8800s I doubt they'd feel a pressing need to eclipse them.
Then again, if ATI drops a sizeable bombshell onto the market, boasting, say, a 10-15% increase in performance over nVidia's flagship, that might change things, mightn't it?
All of this, of course, is hypothetical. In any case, I wouldn't hold out hope for the 9800 until ATI makes a move. Just doesn't make any sense from a financial perspective to eat one's own young.
Just some thoughts.