It has been reported that the upcoming Intel 300 series chipset motherboards will not be compatible with the existing Skylake and Kaby Lake CPUs, nor the Coffee Lake-S CPUs to be compatible on Intel 200 series chipset motherboards, despite the fact that both are actually using the same LGA 1151 CPU socket.
Hardware.info are among the tech sites that are given the early access privilege to the Intel's upcoming Coffee Lake-S CPU and 300 series chipset motherboards, has conducted a test to confirm the claim.
The photo above was taken from Hardware.info, a side by side comparison for Kaby Lake CPU (left) and Coffee Lake-S CPU (right). The test conducted involves fitting the CPUs into motherboards with the incorrect chipset, to see if there's any chance to boot into the system at all.
From the test, the guys from Hardware.info confirmed that having an incompatible CPU on the motherboard will not result in any damage to the motherboard nor the CPU installed. They managed to power on the system at most, however, there is no way to boot into the system at all.
(Source: Hardware.info)