with both copyrights and patents, fees should be just rise geometrically, yearly (but can be prepaid into the future). so for instance, the first year might be $1000, the second, $2000, and the 10th year, ~$1MM (a 2^n progression). by year 20, nearly every patent and copyright would be relinquished as the fee would be ~$1B. with those kinds of rates, even disney would have to innovate to stay large and relevant, rather than sitting on their laurels and collecting rents in perpetuity.