If you aren't playing new games, upgrade your CPU. 6700K is still an okay CPU but even now, and great for its time, you're bottle necking your 1080 at this point. If gaming is all you do, get 5600x or an equivalent i5. You don't have to spend a lot to get the most out of your 1080 and a few more good years out of it. I'm still on my 1070ti. My plan is to drop in 5800X3D to replace my 1800X and snag up a used 6800 whenever the new cards come out. I suspect that will get me another 4-5 years without a major system overhaul.
Full disclosure, I'm an AMD guy so take what I'm about to say with whatever grain of salt you have near by, but this is what I would do. Since you need a full system upgrade ANYWAY, I'd wait until the new AMD socket is released and go with a Ryzen. You can get a few generations out of your hardware and even drop in a new CPU later down the road if you don't feel like doing a complete rebuild. I also feel it's most cost effective long term.
Instead of having to buy new ram and motherboard and who knows what else, I can take that money to either spend on better hardware or just pocket the extra change.
TL;DR, wait until next gen comes out and decide what fits your budget paired long term performance goals. I'm already on 5 years with my 1800x and 1070ti and I expect to get atleast 4 more out of a CPU and graphics card upgrade. All told, after the upgrade, I'd be into this platform for $3000 over about 10 years which, at $300 a year, is a STEAL.