The vast majority of the value an artist realizes from his work will almost always be within the first decade, and few artists will base their decisions on whether or not to produce a work on the possibility of future technologies or legislation that might enhance their value.
Indeed, trying to extend copyrights endlessly to "protect" artists whose works are made valuable by new technology are far more likely to stifle innovation because the original artists or their heirs can't be found than they are to encourage innovation by letting artists know that in the event some new technology appears 50 years off their heirs might benefit (if anyone can find them).
One thing which is particularly galling about today's copyright rules is that it is often impossible to identify the copyright status of a work; as a consequence of this, the public domain is actually shrinking and unless things change it will never grow again but instead shrink to a mere fraction of what it is today. For example, suppose I find some black and white film footage I like in the back of a closet, but the only thing I know about it is that it existed sometime prior to January 1, 2000. That footage may have been in the public domain for half a century or more, or it may still be protected under copyright 150 years from now (even without any more changes in the copyright rules). If the film's printed on gunpowder stock, it's almost certainly public domain (since nobody's used that for a long long time), but if it's printed on safety stock it could be anything.
Too bad there's probably no practical way to repeal the Berne Convention or its successors.
Too bad there's probably no practical way to repeal the Berne Convention or its successors.
All treaties can be nullified by an act of Congress. Not that I suggest that this is necessarily a good idea, but it's actually quite easy to do - a simple legislative majority is all you need.