The dust never settled in technology land when it comes to popular component hardware. AMD is making rounds in chatter on the web, Ryzen 4000 with ZEN3 would/could be announced as soon as September already, and that would be way ahead of schedule. 

So the rumor now is that AMD is moving forward with the processors to be presented in September. AMD itself wanted to launch the project in 2020. Another source contradicts this and says it will be 2021. September would coincide with the new date for Computex and Computex is taking place from September 28 to 30. Perhaps there the announcements with the release in Q4.

 The fourth generation of Ryzen is based on an optimized Zen-2 technology that should start in September, says a report from the usually well-informed industry service Digitimes. The processors, codenamed Vermeer, will be an evolution from Matisse that is above all an optimized fabrication process from 7nm towards 7nm+. AMD themselves already stated that the ZEN3 processor would see an IPC uplift of 15%. 

From what we are hearing there will be an architectural change, the CCX design. What exactly the change will entail is not shared, but here rumors indicate a CCX design of 8 instead of 4 cores. The new arrangement offers better utilization and access to the entire L3 cache of the CPU. (512 KiB L2 and 32 MiB L3). Personally I doubt this as such changes are expensive to implement, also you'd be looking at a more monolithic design, which is not something that AMD has been pursuing for a long time. Then again, that extra 15% IPC needs to come from somewhere.

On a recent Financial Day, AMD confirmed that Zen 3 is coming in late 2020. Sources from the mainboard industry have now specifically mentioned September to Digitimes.