I would say a fair compensation for the original work is fair, until certain threshold, after which they must invent new thing rather than continued benefit of an existing. Say once they earned 400% of valuation or cost of invention or similar. there could be a system in place. But of course the people to regulate this has a natural bias, as they themselves would be hurt by it, most likely. So the vast majority, ie. the public is at an disadvantage, greed wins again.