Z170 boards supported Skylake and Kaby Lake(with firmware updates).

Disappointing that those boards won't see the new more cored processors.

There's some... interesting power consumption with the latest i9 OC'ed. https://www.eteknix.com/intel-core-i9-7980xe-extreme-edition...

I miss the days when there was actual competition with chipsets. Intel seems way too keen to put harsh restrictions on their chipsets for anything but their most overpriced chips, especially W.R.T. PCIe lanes and ECC support.

Officially, Z170 won't see Coffee Lake. Unofficially... Let's just say it's possible.

Is there some proof you could share? Motherboard manufacturers have been super silent about this.

Sorry, not really, I've only heard rumours (from a reliable source though). It should be technically possible because coffee lake CPUs were demoed on previous chipsets. I doubt you are going to hear much from the motherboard manufacturers, they're probably more or less obliged to push the Z370. I understood the unofficial part as in not publicly available, at least not right away.