The PCIe 4.0 interface comes with twice the bandwidth of PCIe 3.0, but that also comes along with tighter signal integrity requirements. Unfortunately, Intel reportedly ran into issues with the chipset and untenable amounts of jitter (we're told the Comet Lake processors themselves are fine), thus requiring cost-adding external clock generators to bring the interface into compliance. In either case, the issues reportedly led Intel to cancel PCIe 4.0 support on the Comet Lake platform.Comet Lake is expected to be introduced around mid-April. The platform reportedly got delayed due to the issues with PCI Express as well as unidentified challenges.
Rocket Lake in 2021 may be the first Intel consumer chip with PCI Express 4.0 support.