In a thread over on Overclock.net, it is reported that a 6-core Coffee Lake CPU has been bootable on an MSI Z270 motherboard, though no benchmarking data has been released to prove the stability of this configuration at this time.
While granted this modding system has brought about the question whether Intel created a new chipset for no reason, I will take it with a pinch of salt due to above, no proof it's stable or performs on par with 300 series boards. I can't see the hexa cores being a problem though. Z270 boards should have the power delivery headroom that allowed for huge OC'ing potential which should satisfy Coffee Lake's power hunger
I would make sure you count your fets and do your homework first. Otherwise you may not need any central heating, as you could burn your house down.
The only part of Intel not making CL compatible on older boards I agreed with was the "Bulldozer" issue. IE - AM2 boards do not have the fets or cooling needed for Bulldozer, but board manus just did it any way resulting in many MSI boards catching fire.