They can make it “mandatory” but if it sucks then people will just change their DNS to something else. The people who don’t know how to do that probably don’t leave the mainstream internet anyway.
25 years ago I also had a lot of trust in freedom on the internet, because it would just "route around censorship" and all that. I don't have the same confidence anymore.
The internet seems to be doing just fine at routing around censorship. I can still access TPB and Libgen a multitude of different ways despite the efforts of my govt to block them.
DNS is harder to block because it’s not illegal, and it’s a core internet service, which means there’s a lot of interest in preserving access.