After emailing AsRock and Asus, it sounds like they are not going to be offering new workstation boards specifically for Kaby Lake E3 v6 Xeons, since the Skylake boards are essentially the same. They would just be BIOS-flashed for Kaby Lake CPUs.
Does this sound correct? Would MoBo manufacturers skip Kaby Lake and go directly to Coffee Lake?
Are there any new features in Kaby Lake CPUs that couldn't be accessed in a Skylake motherboard?