The move follows Chipzilla’s Alder Lake release which does that sort of thing and looks rather good.
According to Phoronix.com the move to hybrid can be seen in changes in updates to the SMCA (Scalable Machine Check Architecture) driver code for future AMD CPUs.
Patches applied add new SMCA bank types (and error descriptions), and also make layout changes, noting that: “Future AMD systems will have different bank type layouts between logical CPUs. So having a single system-wide cache of the layout won’t be correct.... Future AMD systems will lay out MCA bank types such that the type of bank number may be different across CPUs.”
Basically this could be tinkering being to help deal with the mix of cores (big and little, or performance and power-efficient) used with hybrid CPUs.
Intel does seem to be onto something with its use of hybrid CPUs which use the efficiency cores when idling (or for undemanding tasks), and keep power consumption to a minimum which is great for laptops and battery longevity. Efficiency cores can also contribute to overall performance levels when needed, making them useful in desktops PCs as well.