Something like that's already been thought of: Alessandro Forin's eMIPS project a few years back developed a prototype processor with a small FPGA fabric direct

Something like that's already been thought of: Alessandro Forin's eMIPS project a few years back developed a prototype processor with a small FPGA fabric directly embedded into the processor that allows for creating custom instructions per application, e.g. https://www.researchgate.net/publication/255563459_A_Framework_for_Automated_Acceleration_of_Application_Binaries_on_eMIPS https://www.researchgate.net/publication/255563459_A_Framewo... among others. I don't think anything ever came of the idea; I imagine there's sharp limits on how much can fit into a CPU while still having decent performance. > "The ability to modify the data paths in a set of general purpose processor components (e.g. register banks, caches, integer ALU, float ALU, vector ALU, pipeline lookahead, etc) for specific applications by modifying the microcode would be a real leap forward." The latency and die cost of the connectivity for being able to rewire a "sea of execution units" is going to kill clock speed and performance.