I think you may be misinterpreting “possible” here. I’m shocked that it’s possible to get funding and interest to make a 639 year piece happen. It is unclear if it will be possible to complete. I do not think it would be possible to make a 10,000 year piece happen.

As with all things, the contraption is not the hard part. It’s the supporting civilization, society, economic context, and will of generations of people.

Cage’s game here is to question the entire scaffolding of art, not the pigments of the paint.