Taxing that much revenue would indeed be painful for a house that was still making buckets o' cash off of a long time property but would do little to get small, slow and low-selling items released that they still hold but refuse to turn to PD due to "we paid for it, it's ours even if we don't use it".

As long as its' wishful thinking, I'll stick with the "doubling tax". 10 years after publishing (or immediately if the creator sells the rights) copyright licensing for said items is... $1. Next year, $2. Then 4, 8, 16, 32....you get the idea. The longer it's held the more more it costs. Something like this would at least get the majority of them released sooner than, um....never?