Each headstone represents a line of descent that will not continue. Not a person who died, but a lineage that ends. The marker might list the earliest known ancestor and the last descendant, or simply note that the line terminates here. What is being memorialized is not a life, but a future that will never exist.
The goal would not be judgment or blame. Lines end for countless reasons: chance, choice, illness, migration, history. This would be a quiet space for acknowledging that extinction happens not only to species and cultures, but also to family lines, and that this kind of ending is usually invisible.
By using the familiar language of a cemetery, the idea makes an abstract concept concrete. Walking through it, you would be surrounded not by the dead, but by unrealized continuities. It is less about mourning individuals and more about reflecting on fragility, contingency, and time.
What do you think of this idea?
https://www.familysearch.org/ might be relevant for further research.