AMD has said clearly that it isn't going to do an Intel and create a separate architecture for its Zen CPUs that will act as smaller, efficiency cores. What it might do instead, it seems, is leverage its upcoming Zen 4 architecture for those smaller cores. A rumor leak from YouTuber Moore's Law is Dead, claims that AMD is working on a Zen 4D design, which cuts back on some of the features of Zen 4, to pack double the number of cores into each chiplet.
Zen 4 is still planned for the major deskjtop release, we're told, but Zen 4D will come after as a potential fork with Zen 4 and 4D cores on die, for much greater multi-threaded performance. The first design to leverage these cores won't be mainstream chips, but AMD's already impressive server CPUs, with it's 2023 release of Epyc Bergamo reportedly included 128 cores using this design. It's not known if it can do simultaneous multi-threading, but if it can, that would be an absolutely ridiculous CPU.
MILD also claims that 4D cores will act as the little cores on future Zen 5 designs, leading to 8 Zen 5 + 16 Zen 4D designs for absolutely monstrous multi-threaded performance on mainstream hardware. Intel will have gone through a couple more generations of its own by then, but it looks like with AMD making these kinds of moves, the idea of mixing and matching processor cores on a single die is here to stay.