Yes, renaming exists in modern cores, but where do you think the physical values are stored? Answer: there's still a "physical register file". The renamer maps

Yes, renaming exists in modern cores, but where do you think the physical values are stored? Answer: there's still a "physical register file". The renamer maps logical register slots to PRF entries. This is well-covered in academic comparch literature from the 90s onward (and is how it's done in real modern OoO cores too, see e.g. articles on Intel Sandy Bridge). (disclaimer: I'm rebutting the general point about microarchitectures and register files/SRAMs, but haven't studied the Mill in any depth...)