Depends on the technology.
We're not sure how fast the new generations of CPU/GPU will be.
I personally strongly hope that we will research some new tech over next few years that will allow us to
speed up our components raw power exponentially.
Right now we are on our knees with few % increases in single core clocks.
I'd say i7 7700k combined with 16gb of RAM and 1080 GPU or equivalents of those will last around 5 years
considering current increases in performance/year.
1080 could drop to mid/high settings over next 3 years, where 1060 will be below.
It also depends on software side of things.
Developers could write new engines, optimized to current technology (more cores/threads).