How would miners demand? They can't say "do it or we'll stop mining", there will be plenty of competition out there willing to take their job. As for deploying

How would miners demand? They can't say "do it or we'll stop mining", there will be plenty of competition out there willing to take their job. As for deploying the code themselves - it's not like you can deploy it and force people to use it, every individual user decides which client or version of a client to use voluntarily. They would have to convince people to switch to their fork.