According to ASUS it seems that Intel’s new Coffee Lake CPUs could in fact be used with older Z270 motherboards. In an interview with Bit-tech, ASUS ROG motherboard product manager Andrew Wu when asked why the new Coffee Lake CPUs aren’t compatible with the previously released Z270 platform, explained that it” (…) depends on Intel’s decision.” Andrew Wu also went on to mention that Intel’s stated power delivery reasons don’t “make much difference”, and that ASUS themselves could make their Z270 motherboards compatible with Coffee Lake. For that, however, they’d need “(…) an upgrade from the ME [Management Engine] and a BIOS update”, for which “Intel somehow has locked the compatibility.”
When Coffee Lake was announced we were told the extra “pin-count” had to do with power delivery to the two extra cores on the CPU, but I guess that does not really matter if ASUS was able to get a Coffee Lake CPU running on their Z270 motherboards. Now the question could be raised that Z270 platform motherboards might not have had enough power delivery for six-core chips, especially when it came to overclocking.
I think that Intel could have allowed for Coffee Lake CPUs to be compatible with Z270 motherboards, but power delivery could be a little sketchy. Also we’ve been hearing that 8-core Coffee Lake chips are on the way so when those do come out you would more than likely need the power delivery that the Z370 platform offers.
So if Intel did allow backwards compatibility it would most definitely eat into sales of current Z370 sales as many people would choose to just buy a new chip, not a new chip and motherboard. So they have locked compatibility of Coffee Lake to the Z370 platform, which makes sense, especially if 8-core Coffee Lake chips are on the way which will require even more power.