> Actually, I wonder if it would be possible to design a chip with both an ARM and a RISC-V decoder on the same die and just fuse-off the ARM die on select units to avoid any fees...

That's not quite what Raspberry Pi did with the RP2350 (the ARM and RV cores are wholly separate) but they did include the ability to fuse off one side or the other, so I wonder if they'll release a cheaper RV-only version at some point.