I am very excited about this game and I happy to bring my small contribution to this project.
Last May I visited the island of Malta and it gigantic Neolithic temples (oldest complex stone structure in world I think).
Something interesting about these temples is that after the colapse of their builder civilization, the next people use them for other purpose : burial ground or storage for exemple.
I think it could be a good idea to implement this feature into the game, for exemple an old quarry which run out of stone could be turn into a burial ground, same thing with old temples when the religion of the tribe change.
I would like to have your opinion about this idea and if it this easy to add in the game (I thought a update button on existing building could do the trick).