Intel's Z390 chipset is expected to be introduced in the first half of 2018 and word is going around that one of the new features will be support for eight-core mainstream processors.
According to another leaked roadmap, Intel Z390 motherboards are to be expected in second half of 2018. Since we are seeing this Z390 leak already in November (~220+ days before 2H 2018), one could say that the timeline could have changed, so in other words, the Z390 may launch sooner.
It’s also worth adding that Eurocom representative claimed that Z390 motherboards will support 8-core mainstream CPUs. So far there is no trace of such SKU, even the CPU in this leak is a 6-core processor, but at least now we know Z390 supports more than just 8-core CPUs.