This confirms the Z390 will be backwards compatible with current Coffee Lake-S processors, it has the same LGA1151 socket as current 300-series motherboards.
Based on rumors, it appears you will need the Z390 if you want to use Intel's upcoming eight-core Coffee Lake processors.
The website speculates we may see the Z390 platform launch within a month or two. We may hear more from Intel at next month's Computex 2018.