I can't see the world ever getting to that point as long as there is a "real" (silver/bronze-age) Superman in it. The idea of a ban would never occur. If you can't picture it happening in a George Reeves episode, then it would never happen.
That's a big compliment to the George Reeves show, and fully justified as far as compliments go.
Except that George Reeves' Superman is not exactly the Silver Age/Bronze Age version. He's the George Reeves version. If you have watched and liked the first season of George Reeves' version (and I know you have), you will see that (in my view) he's the version best-suited to the world of "The Dark Knight Returns". He would fit right in there, probably embarrassing Batman with his two-fisted clean-up of the underworld and government corruption. George Reeves' Superman would probably be in his element. He would give the mutant leader in the mud-hole a worse beating than Batman gave him, and break a couple more bones besides.
George wouldn't go clandestine; he would be out there, slugging away and inspiring the man in the street.
The Silver Age Superman is a whole different kettle of fish. Not so different that they are not equally admirable, but one thing the proponents of the Silver Age Superman forget is what sort of a world he lives in. The public, for one thing, are as fickle as the most popular girl in high school. They can and have turned on the Man of Steel for the shakiest of reasons. With government propaganda in overdrive (assuming Superman bucked the system), how long before Silver Age people are throwing rocks at Superman in the street?
And that's what this is about. Superman transplanted to an unpleasant society where his own assumptions about his popular influence are thrown into doubt; which means it's also about what I said before: Superman's self-imposed limitations. George's Superman would not take half of what the Silver Age Superman put up with from the general public.