I'd be happy with a copyright system where the fee is $5 for the first year of government-protected monopoly, $10, for the second, $20 for the third, and on and on at the rate of $5*2^n for as long as they like. Note that at the fifteen-year mark, the renewal fee for another year of copyright enforcement would be over $30 million, which seems appropriate.
edit: math
However, since DC Comics still holds a trademark on Superman, you can't use Superman for anything else. In fact, when I bought a VHS tape of the Superman cartoons back in the 90s, the manufacturer was careful to use an actual Public Domain image of Superman on the box. If they created a new image, the Superman trademark would have applied.
Trademarks indicate origins of goods/services. Unless they used the trademark in a way as to convince people that the video originated with DC Comics then they're supposedly fine.
It's a notional consideration but after the lapse of a copyright the "man in the street" should be expected to be aware that the copyright has lapsed and so to be able to buy previously restricted works from any company. Images adapted from a PD work then should be allowed, provided there is no effort made to use that image in an otherwise infringing way.
Of course you can be sued for anything and DC Comics would most likely enact a very expensive lawsuit - in a sane legal system however they should probably lose, especially if they were attempting to use their trademark to prevent the release of material which would have been copyright infringing before the lapse of the copyright term.
If the estate of a creator of a work can use TM law to prevent PD works from being adapated and used then that cancels the deal made in copyright between the state and the creator whereby the works have a presumption of fully entering the public domain.
[Does anyone know of any caselaw covering situations where a major element of once copyrighted - but now PD - works is also a valid trademark?]
It's about suppressing the ideas that copyright is a granted right, a temporary right, that everything starts out free (as in freedom) and is only temporarily monopolized for the betterment of society, that the public domain exists.
And to reinforce that idea that culture, art, entertainment are products owned by corporations which must be paid for.
So is ownership of land, when you come down to it. We like to pretend, in most countries, that land tenure is absolute and that it's the foundation of society, but it isn't. Only a sovereign has absolute land tenure, and the only sovereigns in the modern Western world are corporate entities called governments. (A constitutional monarchy is pleased to pretend that certain individuals are sovereign, but in point of practical fact a crowned head can be deposed by a functional constitutional government.) Everyone else holds tenure contingent on their sovereign not exercising eminent domain to take the land from them and use it to its own ends. Sure, you'll likely get paid, but you don't have the option of turning down the offer and keeping the land.
"Stable ownership is the gift of social law, and is given late in the progress of society." -- Thomas Jefferson
http://press-pubs.uchicago.edu/founders/documents/a1_8_8s12....
Appropriate to who? Maybe Disney, but not for the vast majority of people who are creating works every day. Just yesterday, we had a guy doing a Song a Day make the front page: https://news.ycombinator.com/item?id=6966581. He started it in 2009. Doing very rough math, that puts his burden as:
2009: 365 x $5 * 2^5 = $58,400
2010: 365 x $5 * 2^4 = $29,200
2011: 365 x $5 * 2^3 = $14,600
2012: 365 x $5 * 2^2 = $7,300
2013: 365 x $5 * 2^1 = $3,650
TOTAL: $113,150
It was also extremely painful to search for renewals until all of the renewal records were digitized by the Project Gutenberg Distributed Proofreaders. Now it's just moderately painful, because you have to be alert for variations in titles and author names.
Periodic -- say, every 7 years -- renewals with exponentially increasing costs to renew.
A token fee would do that for abandoned works, but it wouldn't do it for works which weren't being actively used but which the owner also didn't want others to use -- an escalating fee would be better than a token fee to discourage such buried works.
Copyright covers an enormous range of output. Keeping a central ledger that tracked the copyright status of hundreds of millions of items would be a massive undertaking.
I don't think it's unreasonable for Disney to still hold copyright on Mickey Mouse (that might be the nostalgia talking), but there are plenty of creations from much more recent times that have long overstayed their welcome in the copyright protected realm.