According to pictures and screenshots originated at Baidu and spotted by Videocardz.com, Intel's Core i3-8350K was seen running on MSI's Z170A Xpower Titanium motherboard with modified BIOS and microcode changes.

Although the mod does not work perfectly as the iGPU is not available and the primary PCIe slot is not functioning, this clearly shows that Coffee Lake CPUs should have no problem working on Z170 Express chipset motherboards and power delivery modifications, which was Intel's reasoning for lack of backward compatibility, but it does not have anything to do with it.

Asus has already confirmed that the lack of support for Coffee Lake CPUs on Z170 chipset motherboards was pushed by Intel and the latest leak pretty much confirms it.

Of course, it is highly unlikely that Intel will change its decision.