In case you haven't noticed, we are in the midst of a core war, with the enthusiast segment serving as the primary battlefield. It's within the high-end desktop (HEDT) space that AMD and Intel like to flash their biggest and baddest guns, known as Threadripper and Core-X, respectively. With regards to the latter, it's rumored that Intel will introduce a Z399 chipset for its next round of HEDT chips.
Z399 would supplant X299 for whatever Intel has on tap after Skylake-X. That's a bit confusing, though perhaps unavoidable at this point since the chipset space has become somewhat of a convoluted mess. The reason Intel is said to be considering Z399 instead of X399 is because AMD has already staked a claim on the latter for its Threadripper family.
We don't know this to be 100 percent accurate. The rumor originates from PCBuildersClub, which claims it heard about Intel's plans from a "source at a major computer manufacturer." That same source also apparently said that Z399 is ready for production, though it is not Cascade Lake-X, but a simple refresh of Skylake-X.
If true, that means we will have to wait a bit long for Intel to introduce a 28-core processor the consumer space. In the meantime, the refreshed Skylake-X lineup for Z399 motherboards will top out at 22 cores, according to the unnamed source.
You may recall that Intel kicked up a hornet's nest of criticism when it demonstrated a 28-core CPU running at 5GHZ at Computex. it was later discovered that Intel was actually showing off a 28-core Xeon processor based on its Skylake-X architecture with some heavy duty cooling behind the scenes. Photos emerged of Intel carting off a Hailea HC-1000B, an industrial water chiller that can move up to 4,000 liters per hour and uses R124 refrigerant to keep water at a chilly 4 degrees Celsius.
If the latest rumor is accurate, both the Z399 chipset and Skylake-X Refresh will launch sometime this fall, with a 28-core Cascade Lake-X chip slated for 2019.