That is an interesting and difficult problem. What if it were framed a little differently, though: Suppose there were a federal licensing tax. You'd pay, say, 5% of licensing revenue to the IRS for the first 20 years, 25% for the next 20 years, 60% for the 20 years after that, and so on. Obviously these are made-up numbers, but the idea would be that an increasing fraction of the license revenue would go to government.