+1
Crossfire/SLI has mostly always been just willy waving though IMO - it's never scaled 1:1, has many compatibility issues and most of all, turns your PC into a raging inferno heat/noise wise. Custom watercooling can solve the noise issue, though you'd need a professional aircon system to solve the heat issue.
The sooner Crossfire/SLI die the better IMO. It's never going to see mainstream adoption due to price, and so will never seen mainstream developer implementation.
Only once cards drop to £100 each will see any significant adoption, and I can't see NVIDIA selling 1070/1080's for £100 anytime soon, can you?