I know that I am going against the flow, and declaration of many, but I feel that we will never have a Smart City.
Smart is not a destination, at least in my view. It is a long, and winding, road that has to be followed. As new needs surface (population increase, changing culture, new challenges) new solutions will have to be found and pursued. At the same time the relentless evolution of technology (we do not see an end in this century) makes new approaches and solutions available that are more effective and that make existing solution no longer optimal. Still, the deployment of a new technology may be unsustainable (too expensive....) and that city will be stuck with what it has, although it is clear that a better infrastructure would be feasible. Hence that city is no longer as smart as it can be. And if you are not as smart as you could be, you are no longer smart.
This is typical of any historical period, it is just that in these last fifty years the pace of technology evolution is such that during the deployment of a solution you already see that a new one is or will be available pretty soon, making the one you are busy to deploy obsolete.
Hence, I feel it is important to look at the direction, at the path and be smart in pursuing it.
There are a (very) few cases of cities being designed from scratch to be smart. They are built in a greenfield. Cities like Masdar and Songdu are the most recent ones. So far they are more tech labs than really liveable cities. They miss a soul and that is something you cannot build. It takes decades, often centuries, to become the expression of a city and as you walk along those high tech streets you feel that something is missing.
Any trail leading towards a smarter city is rooted in the past, is affected by the should of that particular city, that is why every city has its own way of designing and creating its future. If you don't recognise this you are bound to fail. You might end up decreasing the city pollution or needs for energy but you are not increasing the well being of its citizens.