Copyright is easy to appraise. Estimate the stream of payments it will generate; take the net present value using an appropriate estimate of a safe interest rate.
Will it always match the actual value? No, of course not. Sometimes popularity changes a lot, or interest rates change a lot.
I'm not sure you really need a proprerty tax on copyrights though. They generate taxable income until they expire. It seems more fair to tax the actual income rather than appraised value, to avoid problems from cases where the appraisal is too high or too low.
So of I write a novel and never publish it, how should its value be calculated?
If what matters is actually revenue, well, revenue is already taxed when it’s incurred. Suppose there is no future revenue, do I get the tax back eventually?
If you never publish it, and it's never published after your death; objectively it produced no income and has a monetary value of $0.
With no offense to you or your novel; I would appraise an unpublished novel by an unknown author at something like $100, which might be too high. Some turn out to be worth much more, but most will be produce $0 or less for the author's estate.
How is that tax going to be assessed and by who? What constitutes a novel or a book over a set of well written notes? This whole idea is ludicrous, are we going to raid people's homes and audit their computers and notebooks to see if they've written anything that might be valuable? Just tax their income. We already do it.
McDonald's trademark is not a copyright, so that's a different process. The trademark is appraisable too, but it's trickier because trademark doesn't expire and the stream of payments may not end. You can look at the history of franchise payments as one measure, and consumer revenues as another measure, but you'll need to discount for the actual product. The corporation broadly accounts for the value of the trademark and other things in Goodwill on the balance sheet.
For a copyrighted work, you would examine the work, find similar works, what were the stream of payments for similar works. Take into account age of the work, the artist's other works, etc.
McDonald's does hold copyright in many things. But many of those are unlikely to produce significant income; training videos, promotional materials, etc don't tend to sell for much if at all.
If you needed to appraise a new song by a popular artist, you could do a reasonable job by looking at the stream of payments generated by their average song, and projecting future payments based on the general trends of payments for songs over time. You might also consider current popularity of the artist/song and how that impacts longevity; songs don't acheive many sales initially often hit zero sales and never come back, whereas songs that chart tend to have continued, if meager, sales for a long time.
Trademarks are IP; I thought we were taking about a generalized IP tax.
But, ok, copyright.
Who exactly is going to do these audits, find comparable works, etc? For every single copyright (500,000-ish registered in the US per year, far more unregistered but real copyrights)?
And you’d need to audit all existing copyrights… that song may have produced very little revenue, but then a big artist covers it, and the composition rights (but not performance rights) are suddenly worth a lot more.
It all seems like an exercise in applying engineering to law, which never goes well.
Will it always match the actual value? No, of course not. Sometimes popularity changes a lot, or interest rates change a lot.
I'm not sure you really need a proprerty tax on copyrights though. They generate taxable income until they expire. It seems more fair to tax the actual income rather than appraised value, to avoid problems from cases where the appraisal is too high or too low.