More expensive motherboards do have (presumably) MCU based flash tools so you can upgrade the motherboard via USB without a CPU. But this is a low end A series

More expensive motherboards do have (presumably) MCU based flash tools so you can upgrade the motherboard via USB without a CPU. But this is a low end A series chipset board, it's going to be designed to be cheap, so extraneous features like that aren't going to be fitted. There probably is also some sort of "header" to allow programming Flash in the factory, but it's going to be a set of test pads that need a "bed of nails" or similar to use. I suppose you could standardise it and make it easier to field use (others mention tag-connect cables), but it's such a niche use case I'm not sure anyone would spend the time on standardising it.