Then you would not get rights to the new version number, but you could get it to everything else... excepting that that is a bad example as version numbers would not be copyrightable as a brute fact, but more realistically, if you merely add one creative paragraph of flavor text the clock would start anew on that paragraph, but the protection would not magically flow backwards back in time to the entire rest of the content.

Personally, I think the main problem with copyright is not the things were the owners care about them, but where they do not.

Personally, I would be mostly happy with current copyright, with an extension that items must be reregistered every 5 years, and available for sale. That would deal with the huge amount of items (games are a good example) where the original owners don't care enough to release the game as public domain, or often can't even be traced.

I'm not sure the trapdoor is necessary. If the changes are in fact trivial (whatever courts decide), people will just copy/use the public domain version.

It doesn't really matter - as long as someone keeps hold of what was actually released 20 years ago, they can use that, and it won't matter that the release from 19 years ago remains under copyright.