Actually you were talking about replacing the entirety of System RAM.
The Names of a process have very little connection with the actual physical size of features.
Samsung seems well on it's way to 3nm. They already have an early design kit to share with customers:
https://hardforum.com/threads/anandtech-samsung-announces-3nm-gaa-mbcfet-pdk-version-0-1.1981638/
I wasnt joking (fully) I mean I get what you are saying but this is from AMD directly
https://www.tomshardware.com/news/amd-3d-memory-stacking-dram,38838.html