It seems someone was able to get a Coffee Lake CPU to actually work on a Z170 motherboard! This was of course said to be impossible per Intel, although ASUS said that Coffee Lake CPUs could be used on the Z270 platform. What is interesting is that this was achieved on not a Z270 motherboard, but a Z170 motherboard. The board in question is the MSI Z170A Xpower Titanium and the processor is the Intel Core i3-8350K.
This mod was achieved via a custom BIOS modification and microcode changes. Obviously this was not done by Intel so there are some bugs, currently the IGP is not functioning and the primary PCIe slot is available.
In any case it is pretty cool that this is possible.