I've noticed that a lot of people who are disappointed with the 1080 are comparing it to the 980 Ti. It appears to be a 20-30% performance increase over the 980 Ti in most games.
The 1080 is not the 980 Ti replacement though. It is a 980 replacement and when you look at it that way and see the 60-70% improvement (101% in Rise of the Tomb Raider) that is a pretty nice jump from one generation to the next.
Expecting to see those 60-70% jumps over the 980 Ti isn't really realistic in my opinion because this is the 980 replacement. I think you will see the kind numbers you were hoping for when the 1080 Ti rolls out.
I'm personally anxious to see if a single 1070 will be able to match my SLI 970s. There are some games that don't support SLI and some games where VRAM has caused issues for me at 1440p.
With current resale values I could sell my pair of 970s for about $400 and get a 1070 with no out of pocket cost. As long as I won't see a performance decrease from my SLI 970s trading them in for a single 1070 with 8GB of VRAM seems like a no brainer.
That putting salt on the wounds really, it's priced above what the 980Ti was at release so it should be compared in that price segment.