The physical footprint of PSU and cooling would still have to be larger to accommodate the increased max wattage/heat, whether the chip is on at any given time

The physical footprint of PSU and cooling would still have to be larger to accommodate the increased max wattage/heat, whether the chip is on at any given time or not. The chip would also need its own memory or some interface to access the main memory, which is built into the M1 chip. And, there would be a ton of firmware and microcode updates and stuff to keep track of and secure which was one reason they wanted to have their own chips.