It appears that there are a few features on Kaby Lake and Zen that require significant updates to Windows 10 to optimally function.
Kaby Lake uses Intel’s Speed Shift technology that make it possible to change power states more quickly than Skylake. Because Kaby Lake can make Speed Shift transitions faster, 7th Gen Core processors based on the architecture can increase and decrease clocks quickly. Speed Shift is hardware enabled but it uses the OS to function properly.
Intel’s Turbo Boost Technology 3.0 with Turbo Boost Max 3.0 technology improves single-thread performance by identifying the fastest core on a particular processor die and prioritising critical workloads for that core. This pushes up the processor’s frequency when needed and workloads are also directed to the fastest possible core available. Support for that technology needs to be in the operating system.
AMD’s Zen-based processors have fine-grained clock gating with multi-level regions throughout the chip. Zen will bring in newer Simultaneous Multi-Threading technology for AMD chips. Microsoft will have to make updates to the Windows kernel and system scheduler, which is more involved than a driver update. Vole did something similar to add proper support for Bulldozer-based processors with Windows 7.
So as far as AMD, Microsoft and Intel are concerned getting rid of support for older systems makes perfect sense. You can’t lock these chips into something which was released seven years ago. Windows 8 is similar to Windows 10 but about as popular as the Boston Strangler it is just not worth trying to update.
While corporate customers might like to remain on Windows 7 and incorporate next-gen hardware into their infrastructure, there will not be many of them. Older versions of Windows and alternative operating systems will still install and run on Kaby Lake and Zen, but they just won’t do the cool stuff.