AMD is keeping to its promise about its support for the AM4 socket. Confirmed by XMG, the ageing socket will support Ryzen 4000 desktop processors. The B450 chipset will get to taste Vermeer too, as will probably the X470 and X570 chipsets too. The Ryzen 4000 desktop series is expected to land in Q3 2020.
https://www.notebookcheck.net/AMD-s-Ryzen-4000-and-Q3-2020-bound-desktop-processors-confirmed-to-support-the-AM4-socket-and-B450-chipset.461803.0.html
Looks like as of 05/11 AMD has came out said the new ZEN3 won't be compatible with B450 and x470 motherboards.