AMD will support the AM4 socket until at least 2020, which is great news for the upcoming Ryzen 2 platform if you just migrated to a new moatherboard. That doesn't mean though that there won't be any new chipsets, and the "integrators list" of the PCI-SIG just confirmed that.
The list from PCI-SIG shows products that meet their testing requirements, and a new kid on the block revealed itself, a certification was received on December 19 for the 400 Series (we're currently at the series 300 X370/X399 etc).
The name is not a code name, AMD is abundantly clear in finishing up a new chipset. PCI-SIG is all about PCI Express of course, the site shows a speed of 8 GT / s for PCIe 3.0, which is an improvement on the PCIe 2.0, 5 GT / s of the 300 Series in 2016. This info also means that PCIe 4.0 and/or DDR5 are not yet in the pipeline (or at least PCIe gen 4.0 is not yet actively tested).