Did AMD officialy confirmed that Zen3 will support current am4 motherboards?
In this news is stated that Zen2 and Zen3 is 7nm and we know that 100% Zen2 will be compatible with current AM4 boards so there is a big chance that Zen3 is also compatible. http://wccftech.com/amd-zen-2-zen-3-7nm-cpu-architecture-details/
From comment section: "From what I've read, everything up to 2020 will be on AM4. So let's hope. I would love to be able to upgrade my PC without buying a new mobo, ram, etc. It's the smartest way to cell new CPUs, simply make it a viable/logical option to do so."