with any cpu you can use a dual gpu
now, the question is, do you want to spend lots of money on a very big psu, on two video cards, hear lots of noise from two gpus and getting lots of heat from two gpus while you use lots of watts that will be seen on you power bill?
most users will buy one powerfull gpu and forget sli, in fact nvidia itself is abandoning the concept in general, only dual sli setups work now and possibly that could change in the future thanks to the fact that most games doesn't support well enough that setup and that the second gpu mostly works at half speed, so is half wasted
buy a gtx1080 to have it wasted, is a bad idea for me