Intel's Z370 Coffee Lake Chipset Blocks Kaby Lake Processors In Firmware
The Z370 is a similar chipset to Z270. On the surface, it seems that Kaby Lake should be compatible with Z370 motherboards. And it probably is—the folks at Guru3D say that several motherboard manufacturers have stated privately that there is no physical reason for Z370 not to support Kaby Lake, and that it is just a firmware restriction. The mandate from Intel is to block Kaby Lake on A370 boards.
It looks like Kaby Lake owners will have to stick with Z270 motherboards
This is crummy news for consumers, at least for now. Assuming the off-the-record chatter is legitimate, Intel is effectively segmenting the market and forcing customers who buy a Coffee Lake chip to also purchase a new motherboard. Granted, anyone sitting pretty on a Z270/Kaby Lake foundation probably isn't looking to upgrade to Coffee Lake, but should that decision come down the line, they will be looking at a platform overhaul rather than simply swapping out their CPU.
Going in the other direction, some board partners have said that the extra pins used on Z370 motherboards are intended to deliver the necessary voltage to Coffee Lake CPUs. It is not entirely clear if Coffee Lake might also be compatible with Z270 motherboards if not for similar BIOS blocks. Either way, Intel seems interested in separating its platforms, even if technically there is overlapping compatibility.