Extremely unlikely, for a couple reasons.
For one thing, they aren't going to be "updating" campaign sourcebooks per se. The best Greyhawk could hope for would be a Player's Guide, like the Realms is going to get.
It's also unlikely because we're going to be getting, part and parcel, Greyhawk material in the other books that come out, since its the default campaign setting used in the books, and in some cases, in Dragon and Dungeon.
Finally, Greyhawk isn't quite a supported campaign with WotC in the truest sense of the word, in that it never gets products specifically devoted to it under its own banner. The LGG was the sole exception because of the RPGA's Living Greyhawk campaign, and that's unlikely to be repeated, especially given how that book will still be virtually completely unchanged by 3.5E, since it had so much flavor text.