I'm not sure that duration of the right is a better way to distinguish things.

Taxi medallions are a similar form of regulatory property in that they grant monopoly rights. In New York I believe title vests with whomever possesses the physical medallion and is in perpetuity, but in San Francisco it's more like a license, isn't directly transferable, and has a defined duration.

A few years ago it cost several hundred thousand dollars to purchase a medallion from SF. People often financed the purchase with bank loans. To combat Uber San Francisco dramatically increased the supply of medallions so that the effective value dropped precipitously and is still going down, I think. Many medallion owners are under water, and increased competition from new medallion owners likely caused some people to go bankrupt. (Uber had a similar effect but I'm sure if we tried hard enough we could tie a bankruptcy directly to SFMTA's change of policy.)

I can't imagine a court finding this state of affairs to be illegal or requiring any kind of compensation even though the city basically extracted millions of dollars from people's pockets and then screwed them over. How bad does it need to get before it becomes a taking? It's pretty bad now and AFAIK there's still no actionable claim that can be or has been made. And I don't see how the limited duration of the medallion would matter; if anything a more limited duration implies the purchaser expected to make a return on his investment faster.

Now imagine the city removes all laws that restricted access to providing taxi services. But it still maintained the medallion and the restrictions (insurance, checkups) required of medallion holders. As a practical matter the medallions would be worthless, but you can still say that you own one and are governed by stricter regulations. So perhaps riders will pay a premium (1 dollar? 10 cents?) for that reassurance.

Now imagine a city outright cancels a medallion system. Your metal medallion or piece of paper instantly becomes a curio. I think a court could legitimately say that the regulatory property was impliedly limited by the city sustaining the monopoly. That is, you paid for the government-created monopoly right only in so far as the government chose to maintain the statutory scheme. It's hard to drawn a line between this scenario and the previous two scenarios while keeping a straight face. The law draws arbitrary lines, but that doesn't mean they're entirely divorced from meaningful considerations, like concerns about consistent treatment.

With real property or chattel we can at least pretend that there's intrinsic value to the property, and draw the line at preventing governments from harming that intrinsic value by it taking physical possession from you. Often for real property that's exactly how the line is drawn--you can pay $1 million for a piece of land that you can no longer build on, but as long as you can still pitch a tent a court can legally find there was no taking. (There are other elements that also control, but it's still possible and has happened.) But that fiction is totally indefensible when we're talking about a piece of paper whose only intrinsic value, if anything, relates to the regulatory framework it exists within.

When you look at the law of regulatory takings, where you can't depend on analogies with physical possession to delineate what is a taking or not a taking, you rely on investment backed expectations and similar rules that balance foreseeable restrictions on your property against how much value you've lost by new government regulations. In the taxi medallion case even that approach doesn't help much, perhaps because it would be odd for courts to penalize governments for _rescinding_ laws, and especially for liberalizing restraints on trade.

So given all this context, I can't imagine there being much problem with the government passing a law that says copyrighted works lose _some_ protections when incorporated into published law. Presumably you still couldn't, for example, copy and distribute the POSIX standard in situations unrelated to dissemination and discussion of the incorporating law. The value of the copyright might be significantly diminished, but there's still some commercial value, especially if we assume people will remain law abiding.

And remember that you never _paid_ anything to the government for your copyright. Unlike a taxi medallion, your copyright was granted free-of-charge. Copyright may have persuaded you to make investments, but depending on the kind of property we're taking about, courts can choose to make that fact dispositive or irrelevant--especially when they can invoke the legal fiction that the limitation was always implied and thus foreseeable, and therefore you were an idiot for not taking that into account.

Whatever the boundaries of the law are in this area, I think partial limitations on the scope of your already granted copyright are likely to fall well within the boundaries of acceptable changes not requiring compensation, especially if the carve-out is tailored to serve an honest-to-goodness public purpose.

I think there's a strong argument to made where literally or effectively rescinding the copyright is illegal without compensation. I also think there's a strong argument that doing so would be entirely legal. It's a fascinating question. But neither of those extremes are implicated here.

And note that duration doesn't really figure into any of this, which is why I don't think it's relevant.