With mainstream 6 cores a year and a half away in 2018, I doubt many will upgrade to Kaby in early 2017 if they have anything Sandy-Skylake. 2020's 6 core Tigerlake optimization of 10nm looks to be my next stop.
With my past PCs, the third year was where I got a severe upgrade itch and the fourth year mark was usually where I pulled the trigger on a new build. My i5-3470 is almost four years old and I don't even have so much as a hint of upgrade itch yet.
My Sandybridge i7-2600 is still running strong, I really see no reason to upgrade. New generation of Intel CPU's doesn't mean what it used to 20 years ago. Looks like we have hit a plateau in terms of design challenges and process improvements. That and software technology needs to catch up and be able to use the hardware more efficiently.
Whats really cool though is that kabylake will be pin compatable with Skylake. So if you currently have a 1151 MB, you can drop in the new chip. Will it be worth it though? To get the best out of kabylake you have to go from the 170 to the 200 series chip set so you can get the optimizations that kaby has. The one I like most is optane/xpoint. Ssd's on steroids. 1000 times less latency, greater than 8 times faster. 25 gb transfered in 15 seconds from internal optane ssd to external optane ssd through thunderbolt. I havent yet read about if kaby will be a true upgade on an 170 chipset/motherboard but I bet it will only be around a 5% betterment. Just gotta wait and see if the cost to "blink and you missed the gigabyte file transfer" is worth it. Hopefully the new xpoint /optane ssd's wont be priced at the same premium as sata ssd's were when they were first made available to the consumer. Just gotta wait and see what develop's.
My last system was based off of an i7 I built in 2008. I didn't need to replace it until this year, and mainly because I wanted to build a VR box. Without VR, I suspect it had another couple of years left. Granted, I had upgraded it to use SSDs, upgraded the memory and put in new graphics cards to have it last so long, but that's far cheaper than building new. I used to upgrade my main box every couple of years; how times have changed.
I am still using the Core2 quad 9650. My Deneb 965BE (already 7years old processor, using a DFI 790GX M3H5 Motherboard - which is also a 7year old), and another Core2 Quad 9400, remains viable on Windows 7, as well as Windows 10, for my use. I only upgrade the video card and the hard drive.
Until I see a big kick on the software requirement, or if there is really a need to full upgrade, I will keep this setup for the moment..