I have a family member who has passed away, and I still have his artwork at my office. Your argument sounds very attractive, but then again, how does government institute something that is fair to everyone? Being practical is not a side issue.
If you cannot practically say that this person created this piece of art at this time, and then be able to trace that back so the person is compensated, we are going to have the same issues we see with this other issue. You're claiming there's an intergenerational unfairness when someone exhibits work that was created before the 1988 line versus after.