Everything about future Intel releases is very vague and knowing Intel it will probably change. This is what I have been able to patch up from everywhere.
Rocket Lake-S is a 14nm backport of 10nm Willow Cove architecture used in Tiger Lake. It will be on LGA 1200. It should support PCI-E Gen 4 but it is not certain. Release probably early 2021.
10nm++ Alder Lake-S will sport up to 16 cores in a big.LITTLE-esque cluster of Golden Cove and Gracemont cores based on information available now. It will be on LGA 1700 which should last for at least 3 CPU generations (as a response on AMDs long therm socket support). Definite PCI-E Gen 4 support. Intel should be introducing DDR5 with this generation. Release in late 2021, early 2022.
Ice Lake-SP will be the next-gen of Intel's Server processors. 10nm+, Sunny Cove architecture, Socket W LGA-4189, PCI-E Gen 4, 3200 MT/s 8-Channel Memory. And the next Ice Lake-X will be derived from those for HEDT platform. Release sometime in 2021.