As the internet continues to accelerate our culture, that time is only going to grow shorter. Longer copyright terms may have made sense in the past when distribution was hard, but today's world moves much faster, and the law needs to catch up.
Now--is that a good argument for such a long copyright period? I don't think so. I think the only time copyright should survive the author's death is if they have kids who are not yet adult.
The intention of copyright is to promote the creation of works. Rewarding authors is the means, not the end. In the case of LOTR, Tolkien didn't write it to provide licensing revenue to his grandchildren; he wrote LOTR because the creation of fantasy languages and histories was his passion and he could make some money from it. A much shorter copyright would have sufficed to inspire the creation of LOTR. Furthermore, the creation of movie adaptations would be helped by LOTR coming out of copyright, not hindered. Disney's empire was built on adaptations of out-of-copyright stories. Shorter copyright would in many ways encourage the creation of more works.
Trademarks clearly should have much longer protection periods than copyright. In fact, a business should be able to operate infinitely under the same legally protected name as long as they remain an active business in good standing and the haven't lost their brand name to a word in common usage.
Now with a mouse click anyone can upload music and books to digital storefronts.
The law has caught up, directly in favor of those who own the majority of successful IP. As culture has accelerated our laws have only gotten more draconian.
I'm all for this fight, but don't doubt that it will be just that, a fight that the victors will write the history of.
Regarding limiting copyright to 10 years, and since you brought up ponies, I feel that solves the wrong problem. The issue I see is that a few large greedy corporations effectively monopolize the copyrights for the vast majority of the nation/worlds creative output, that they then further exploit a corrupt political system to extend those copyrights indefinitely is almost secondary.
A thought experiment: make the sales/purchase of copyright ownership illegal. This would still allow an artist or creator to license the right to sell and distribute their work, but leave them unable to lose (legal) control of such distribution. This still allows a lot of room for the mega-corps to profit, but with less outright exploitation of artists than we currently see. Copyrights are held by the creator(s) for life, and works pass into the public domain after death, not the artists estates (or more often, the organization that owns the copyright). I feel this is simple to understand, fair to creators, and still provides business incentives to non-creators to invest time and money in the production and promotion of quality content.
I suppose you could legislate the general condition, but there will always be edge cases. Unfortunately, allowing for edge cases is going to result in abuse.
The point of copyright is to get works into the public domain by allowing creators to recoup the costs of production and make a little bit of profit, the point is not to allow an endless revenue stream from something that is public domain.
If anything works that create more revenue should have their terms expire faster.
I also support continuously raising the price necessary to renew the copyright as you try to carry it longer and longer. And again, I'm not trying to hurt the mighty Disney corporation; sums they'd laugh at would still be sufficient to open the bulk of the content back up to us, and that's what I care about.
To make my point clear, this is entirely practical. In theory, should Steamboat Willie be public domain by now? Yeah, sure, there's no really good argument based on the public interest otherwise. But as a practical matter, if we could distinguish between Big Copyright's interests and the vastly larger "everything else", we'd be much more likely to come to a compromise that leaves everybody reasonably satisfied, if not ecstatic.
Now, extension of trademark, that I get to a limited degree. They can be the sole Mickey maker for a while. But why should they not have to make new material to generate new income from it?
Say you wrote an open source software package in 2004. Should Microsoft be able to take your work and incorporate it into a proprietary package, just because 7 years passed?
No, you don't get to own an idea forever just because you thought of it first. The very concept of 'owning ideas' is silly, but even if it wasn't, the second you tell it to someone else, it becomes part of the collective society and culture. If you don't like the deal that copyright gives you, you have a choice: don't share the idea at all. And that's fine, and I'm sure that the world would have kept spinning if nobody ever drew up MickeyMouse.
And I don't actually program anymore, so let's go with writing: should anyone have the ability to republish it without my consent after the copyright has ended? Yes. Even a big publisher.
Should anyone have the ability to take my created work and extend on it, using my creations outside of the created work? Yes, after the trademark ends.
I'm sure John Yoo could find something in the Constitution to allow it.