I think one of the main selling points of the 1080 and 1070 for me is they perform like 2x980 SLI and 2x970 SLI respectively.
So it sounds like 2x480 CF = 1080 = 2x980 SLI performance, so the value probably depends on much AMD and Nvidia battle it out as far as pricing of the 480 versus existing 980 stock.