We already know that AMD Zen 3 CPUs based on TSMC’s 7nm+ process node are on track for launch likely during the second half of 2020. Recently, TSMC is already progressing nicely with its next-generation 5nm process node. So this means AMD Zen 4 CPUs are likely released in 2021.
According to recently rumors, AMD’s Zen 4 CPUs could using a new type of memory, which could indicate a jump to DDR5 RAM, and again that would all fit with a switch to a new motherboard. All this remains speculation, naturally.