It is now possible to get X370 motherboards and Ryzen 5000-series processors to work together, albeit only on ASRock Taichi motherboards so far. There is an air of mystery surrounding the BIOS update that brings support for Vermeer processors to X370 motherboards, though.
https://www.notebookcheck.net/AMD-Ryzen-5000-Vermeer-processors-are-now-functional-on-X370-chipset-motherboards.508874.0.html