Maybe it can't be enabled for stability reasons... or the team changed their minds about the historical accuracy of the idea.

Sounds like a real winner of an idea to me. Certain buildings (baths, roads, walls, etc) would require upkeep and it would help keep the late game economically challangine, since advancing cities too much might actually [I]weaken[I] one's war chest.

I hope a team member comes on by; this idea is intriguing.