$389 for a 1070 is approaching reasonable. $300 would make that card be a pretty exciting option, and anyone who doesn't have one would probably have one pretty damn fast at that price.
Also, regarding the 1080ti's memory. I thought it was said to have regular DDR5. Remember that? I guess it was just a rumor of course. If they used that, people would laugh at them pretty hard. A cut down Titan makes more sense. By the time you can actually get one for $700, Volta will likely be a few months away. I won't even buy one for $700. That's a stupid price. I think a $650 price for a flagship is already perfectly expensive and I won't support prices higher than that unless its a full blown, uncut flagship with nothing disabled, and not even the Titan meets that description. Titan is $1,200 and its cut down anyway.
I hope AMD takes off hard with Mgpu and DX12. We need people buying cheap, powerful options like dual 480's to keep the market healthy. These prices are just absurd.