Lets take a different approach with a real world scenario. What would be the difference if BTC somehow was CPU mineable only. Currently the miners invest the total amount of capital they can, and use as much electricity as is available.
The only difference I see is that it would have centralized the manufactures down to two (intel and AMD) and people that need CPU's for computing would be in need driving the costs for processors to extreme levels. By using CPUs you have competing markets.
So in the end you create a chip shortage, market competition increases the cost up to the unaffordable range, individuals still cant participate (hash will always be higher than the average person can provide), you centralize the manufacturing, and you create a hash market where hashrate can more easily be gamed across networks. On top of this the effeciency is lower overall, it costs more watt-hours per difficulty unit lowering the networks difficulty. Even motherboard prices would go up a lot because of the people building cpu mining rigs along with gpus.
I don't like that ASIC's exist and would love to see Btc being CPU mineable only but thee fact is that they do exist, so we have to work in reality.
