A patent describing AMD's approaches to a hybrid ISA solution for low power computing has come to light recently. AMD could be taking a cue from ARM's big.LITTLE approach and Intel's hybrid ISA implementation in Lakefield and the upcoming Alder Lake processors. The patent is reportedly still being tweaked upon, but there is no confirmation that this design would indeed make it to market.
https://www.notebookcheck.net/AMD-could-join-ARM-and-Intel-with-its-own-big-LITTLE-esque-hybrid-CPU-design.485589.0.html