If someone releases DDR5 or DDR6 based PIM, then most of the memory bandwidth advantage of GPUs evaporates overnight. I expect CPUs to be king at inference in the future.
MCR DIMM is like 1/2 the memory bandwidth that is possible with HBM4, plus it requires you to buy something like 2TB of memory. It might get there, but I'd keep my money on hbm and gpus.