Also the way the current copyright system works means those free software licenses are already "dead" by your definition. It's just through pure chance that the duration keeps getting extended retroactively. The only difference between the current system and the proposed system is in the duration and the fact that in the old system all works had effectively the same duration again through pure chance because it's based on the lifetime of the author.
14 years seems plenty enough that its really shouldn't have any real impact on copyleft. Bugs, security patches, and plain reality changes makes 14 year old software kind of unusable. Many applications that is 14 years old won't even start on modern system and hardware.
So, there's this benefit too!
However I don't think it would work in practice, for the same reason public domain suffers now which is corporate lobbying. Fit to purpose, well thought out laws do not survive it.
It's the collective maturity of people that has to change. When the powerful elite is able to value culture more than their personal agenda, we could see some change. But that is a distant future if at all.
Company has an asset whose value increases, that needs to be booked and eventually declared as income AFAIK. I'm really not a good accountant when it comes to IP but I think that's the general idea.
I'd even go one step further, and make it a progressive tax proportional to the duration the work has been copyrighted. Initial grace period of a few years is free, then a very modest rate, but after a couple of decades it starts to ramp up really high. If it's that valuable, you can keep paying it off the profits as long as you want.
Same thing with estates. Inheriting a copyright? Fine - but there's a tax on that (with the usual applicable caps etc).
And said tax receipts could be specifically allocated to, say, fund libraries, free public Internet, and other forms of storing and distributing information and works of art for the benefit of all.