The devs have talked about performance bottlenecks a lot - the real benefit of Factorio on the M1 would be the RAM interconnect, as most of the performance issues are related to RAM latency. Upgrading your PC from (e.g.) DDR3 to DDR4 gives you a whole lot more FPS per $ than upgrading your graphics card or CPU.
Does Factorio benefit more from RAM latency or bandwidth? Apple's processors have unprecedented GPU-like memory bandwidth available to the CPU, but I don't recall hearing about the latency being anything special. (For latency, AMD's 3D-stacked cache might be the best solution out there.)