Microcode? I don't think that's how modern μarch works. You can definitely make modern compute accelerators more like a plain CPU and less bespoke, and this is what folks like Tenstorrent and Esperanto Technology are working on (building on RISC-V, an outstanding example of "simple" yet effective tech) but a lot of the distinctive featuresets of existing CPUs, GPUs, FPUs, NPUs etc. are directly wired into the hardware, in a way that can't really be changed.