> you can sell excess electricity supplies to other cities, lend them public services such as police or fire protection, build mass transit like commuter rail between cities, etc.

That was already possible in Sim City 4. Even in older versions (Sim City 2000 iirc) you had neighbor cities and could buy and sell utilities. Those features work just as well when controlled by AI. There is just no reason not to implement it aside from the DRM benefit.