Why would you wait until the game is extremely complex and nearing completion before you start working on getting the computer to be able to understand how to run the things it needs to run? Something this complex would require that the AI be developed in tandem with the addtional levels of complexity that go into the game.
Having a game that literally plays itself might be a bit much, except as maybe a gimmick where you can watch worldgen creatures build their own procedural cities, but there are obvious reasons why there should be something that allows for AI-controlled "bustling towns" that have villagers go about their daily business, if only for Adventurer Mode. (And this is, after all, a part of the next development push.)
Further, even in Dwarf Mode, there is something to be said for giving the player the ability to automate certain routine decisions. We've already had "Standing Orders" such as ordering more charcoal fired up if you start to run low as a winning suggestion in the ESV.
There is nothing wrong with having routine maintainance of a fortress become automatable. As a game about creativity, however, I don't really think we need to have the game auto-designating the layout of our fortresses, however.