Except browsers today are continuously developed, often with larger strategies in mind. Google has stated very openly that their ideal state is a world where there is no insecure HTTP at all and they intend to move everything as close as possible to that state. To reach this, the browser behavior is slowly tightened over a long number of releases.

So a better analogy would be a carmaker announcing that they don't want people to drive to unsafe areas. They'll monitor people's driving behavior via telemetry and OTA-update the car's software accordingly to nudge people's behavior closer to that goal.

So the warning would probably be the first step. Driving to unsafe areas will still be technically possible but it will become progressively more cumbersome until you just give up.