To be honest i fail to see why the ISPs should be that bothered about people using DoH? Sure they are required by the government to block certain content at the DNS level which is what they are doing. If people use technology such as VPN, proxys or DoH to get around those blocks why should they care?
The ISPs only implemented these blocks because the government required them to do, if the law were to be repealed most of them would probably drop the DNS blocking and history retention as it costs them money to maintain with no benefit to them. And there main goal is to squeeze as much money out of every subscriber as possible not police the internet.
Biting the hand that feeds IT
