The first nine years of copyright are free. After that, you pay $100 to renew for the tenth year. At year 20, the price is $1000 / year. At year 30, the price is $10,000 / year, which is still perfectly reasonable for profit-generating IP.
The 70th year of copyright will cost a billion each year. At that price, it becomes a major board room decision whether to keep milking the same IP or rather come up with something new.
The profits from this tax could go to culture and education, similar to what is done with gambling profits in many European countries that have a state-owned gambling monopoly.