If the clocks are in the 1200MHz range then it's definitely feasible that it could be used to launch a new generation. Given the scaling of Tahiti, with 12.5% more SPs and 30-35% higher clock speeds you'd see a performance increase of around 30%, which is more than the change from the GTX 480 to the 580 brought--that was an increase in performance of 15%.
Also, given how we've seen it pan out in the past, we can expect a 50-65% increase in performance from the GTX 580 to the upcoming GTX 780/785. The HD 7970 is currently 20% faster than the GTX 580, and since it's a new card on a new architecture that means we can expect around 5% more performance with new drivers, making it 25% faster overall. If the HD 8970 is 30% faster than the 7970, that means AMD has the card they need to battle it out with the GTX 780/785.
And given AMD has had a good advantage for at least three years over NVIDIA when it comes to getting out cards on a new process node, the GTX 780/785 is gonna be here by summer or perhaps later if they have too many problems with yields. It's slightly delusional to think the Enthusiast Kepler cards will be here in March/April.