AMD is now ramping up for the move to the DDR5 era which is needed to get ahead of DDR4 issues. DDR5 is much different and not a dumb bank of transistors anymore. Now logic has to be redesigned from the ground up. Speculation over a Zen 3+ product is not likely as AMD is still ramping up Zen 3 which has been stated as the last of the AM4 CPUs.
Zen 4 processors code named Genoa will herald in the DDR5 based processors. The southbridge will also need to be completely redesigned. AMD engineers have been working on this for quite some time now in anticipation of the move.
Zen 4 is expected to launch the next year in 2022 and will bring significant improvements potentially up to 40% over Zen 3 assuming faster clocks can be achieved with 5nm. The CPU today is mostly cache memory, the actual CPU die is rather small by comparison.
One of the reasons for expecting 2022 has to do with available fabrican resources. TSMC is backlogged which may take some time to get caught up. NVIDIA resorted to using Samsung to get Ampere into production.
On the GPU front the RDNA 3 should be popular for gaming as it will allow for a slightly larger number of compute units. The monolithic design of old is more likely to be CFX on the die to solve the problem of complexity in design. The GPU design today is far different from the older designs. The thermal issues alone are a big problem as seen with recent graphics cards.