Sounds like this would just screw the little guy. Warner aren't going to have a problem paying an increasing fee every decade when their works are still bringing in large amounts of money. The people this would hurt are the smaller artists eeking out a living suddenly losing a large chuck of their income.
Maybe the 70 years shouldn't be a fixed number but should vary based on 'sales' each year. Or you lose copyright after a certain 'sales' threshold. That way everyone gets to make a 'fair' amount of money from their works before losing copyright. Easier said than done though.