My understanding is that there is little benefit in upgrading the iGPU to RDNA2 because of the bandwidth limitations imposed by sharing ddr4 with the CPU. We should see some real improvements in iPGU performance once ddr5 rolls out late 2021/early 2022.

Probably just a no need type of thing. The Vega 8 is plenty fine for normal desktop usage, and they already had it integrated into Zen2. So just plop in the new Zen3 CPU and call it a day?

Which is for comparison basically what they did on the desktop side. The Ryzen 5000 desktop CPUs use the exact same IO die as the Ryzen 3000 line.

Maybe they skipped 7nm and are going straight to 5nm for RDNA2 in CPUs. Zen4 based mobile chips will probably be a very interesting release.