I do believe that SLI 1080s, Titan, and the 1080ti will bring 4k gaming into a reality. LinusTechTips already did a video displaying solid 80+ framerates in 4k running the 1080s in SLI.
Whether or not you should wait for 4k is entirely based on if your system has any cpu/psu bottlenecks and such for when these cards make their debut.
And yes, I believe 4k panels will be more affordable every year. As the technology becomes older, manufacturing becomes cheaper, and product costs get lowered.
The future is here, cheers.