Yeah. Also, remember that GTX 780 and GTX TITAN are a few percentage points away. For GTX 780 Ti to be successful, it needs to be at least lower double-digit percentage point improvements, which means super-GTX-TITAN performance.
GTX TITAN will still be their compute/productivity/professional/workstation/gaming hybrid card, which will also be good for those crazy-rich people doing benchmarks and whatnot. But for most people, it'll be useless - it's there mostly for marketing's sake.
I think GTX 780 Ti would probably be 12~15% faster than GTX 780, and it might be sold between 649$ (I doubt it) to 799$. Although, unless it beats R9 290X, I think it'll be priced around 699$ (USD).
For that to happen, nVidia is going to have to drop the price of the GTX 780 enough to make it worthwhile. Otherwise, NewEgg and other companies will have a huge stock of these cards, and nVidia won't have anything to compete against R9 290 Non-X.
So I think GTX 780 is going to sell for between 499$ and 549$ (USD), because that'll put AMD in a lot of pressure. Gamers responded tepidly to nVidia's release of G-Sync and GTX 780 Ti, so unless nVidia can re-heat their enthusiasm, it'll be a tough sale.
Also, remember that the GTX 780 is selling for 649$ right now. A 100$~150$ price cut will be a welcome sight for sore eyes, especially considering this is a 3GB card we're talking about.
** EDIT ** : Hexus agrees with me. http://hexus.net/tech/news/graphics/61405-nvidia-unveils-geforce-gtx-780-ti-radeon-r9-290x-killer/