Funny to see this thread brought back from the dead.

One thing no one seems to really be considering here is, even if the early issues did become public, could another company realistically use them? If all you had to work with was early issues of Action and Superman, could you still use clones? Cyborgs? Aliens from planets other than Krypton? Beings from other dimensions? Evil businessmen? Even if you used original characters, DC still introduced clones, cyborgs, aliens, other-dimensional beings and evil businessmen into Superman's mythos first and those wouldn't be public domain yet. Could DC say "this story uses an alien from another planet, and none of that was in Action #1 so we're suing you!" What about the idea that Lois knows who Clark really is? Could you use the "Clark is who I am" mentality?

If you had Clark Kent act like the "real" person, could DC sue you for that? Sure, they'd have to prove that you're portraying Clark as the real person, but DC would be interested in maintaining as much of the monopoly as possible, and they likely have deeper pockets and better lawyers than Image or Dark Horse or other small time publishers.

Superman has been in constant publication for almost a century, with thousands upon thousands of books to his name and countless more appearances. Only a small fraction of that would be public domain. How many lawyers would you have to hire to comb through each issue, making sure that nothing broke DC's copyright for the stuff they still owned? And after all that, after limiting yourself to the few things the early issues used, after making sure that you're not inadvertently breaking copyright by introducing something.....would you still turn enough of a profit to make it worthwhile? Because I can pretty much promise you, DC would be breathing down your neck every step of the way waiting for an excuse to bury you under a mountain of legal accusations.