Telia did the same thing in Sweden some years ago. There are however ISPs who have a business model based on them having a very high profile in personal integrity politics (like Bahnhof), which I would feel more comfortable with thanany other DNSs
By wouldn’t you expect Bahnhof to offer a DoH-capable resolver for its customers then, that you could use in FF if you choose to enable the feature once it’s out of the experimental phase?