TechPowerUp speculates there could be a chance that Intel's Coffee Lake-S processors are compatible with current motherboards after all. An ASRock representative revealed on Twitter last week that you will need a new motherboard for Coffee Lake, but now users have discovered that a recent 200-series BIOS update from ASUS mentions "Intel Kaby Lake/Coffee Lake-S Host Bridge/DRAM Controller":
This development shouldn't necessarily raise hopes. Although Kaby Lake and Coffee Lake have a lot of architectural similarities, particularly with their uncore components, revised electrical requirements of the new chips could be behind the lack of backwards platform-compatibility. It remains to be seen if you can use your current "Skylake" and "Kaby Lake" processors on upcoming 300-series chipset motherboards.
Hopefully, Intel will clear up the situation soon.