I was looking at a bush recently, and thinking "why can't cities be like this?"

The obvious answer is, of course, building regulations. (And lazy thinking. But we'll get to that.)
Now, I understand that building regulations have a point. Their most obviously legitimate purpose is to ensure the safety of both the building's inhabitants and their neighbors. You shouldn't be allowed to build a house that will collapse if you drive a nail into the wall at the wrong angle; neither should you be allowed to build a house out of flammable materials that will instantly set all neighboring buildings on fire, or fall onto them.
(From a libertarian point of view, you could say that it's only the latter consideration that counts: your buildings should not endanger others; whether they are a danger to yourself is your own problem. But then, almost nobody ever makes a building just for themselves, to be destroyed after their death; in nearly every case, someone else will also be living inside that building at some point.)

Because of this, and because humans are fallible, building regulations usually have large safety margins and limit the range of acceptable constructions to a few well-established principles that have been known to work. Of course, architects and builders can push the envelope by requesting permission for novel types of structures; but that is a lengthy and often expensive process with a high probability of failure, and as such not open to most people.

So, computers.

Existing building regulations are necessarily coarse-grained because they need to be tractable from an administrative point of view. You can't check every crazy hand-drawn plan for static viability and fire-safety and whatnot; you need applicants to operate within the limits of your well-established principles if you want to get any work done.
As long as you're a person and not a computer program, that is.
Imagine an architectural planning program that lets you do anything as long as you don't overstep the bounds of static viability and fire safety. The program would know those boundaries at a high level of detail, and it would be capable of calculating the interactions of far more variables, in many more ways, than could reasonably be be expected of a human being. As a result, the program would be able to permit many constructions that humans would have to fail because they don't understand them.
Now give the program a graphical user interface with tools that make it as easy to use as the Sims construction window. Let people experiment with designs up to the very limits of feasibility. Add a cost calculator -- every construction company will be happy to supply their prices in machine-readable formats if the program allows users to directly export the specifications for every part to the construction service provider of their choice. (Ideally, those specifications wouldn't even have to be implemented by humans, but just fed directly into the machines producing the relevant parts.) Gamify the whole thing and unlock people's creativity, making cities into growing and unique places full of custom-built habitations.

(To answer the obvious objection: Yes, of course it would be possible to code aesthetic requirements into the planning program. No, of course the harshest of critics wouldn't be satisified with any algorithmically encoded aesthetics; but then, those critics won't be happy with anything decided by a human committee, either.)

You might have noticed that I don't actually know much about architecture, and my experience with building regulations is mostly limited to frustration at the impossibility of building an Earthship in Austria. The above, then, is more of an intuition -- an intuition that I think might hold true for other fields as well: that algorithmic decision-making, contrary to the popular imagination, could actually lead to more freedom, by expanding the space of tractable possibilities.

Thoughts?