From the perspective of infrastructure, affordable housing is a tough issue. Most governments, at least in North America, got out of the business of building housing on a large scale decades ago. The central challenge is how to maintain existing public housing stocks. I don't believe that the solution to housing affordability lies in governments expanding their role as a landlords. I do think, however, that some of the innovative partnerships that have been used to build public infrastructure could be looked at as a means to build more affordable rental and purchase housing in large cities. There are some examples of this in Canada such as the Regent Park redevelopment in Toronto, though I would suggest that the private, market based housing there is still too expensive for most, and the public housing insufficient in number. Really what is needed is something to fill the gap: housing for middle income earners. Governments could facilitate this better, as is seen in other jurisdictions, through policy changes, regulation, and in some cases tax breaks and financing tools. I'll write more about this in the future and provide some examples. I'll also write about the idea of smaller, more affordable cities in Canada doing more to attract creative, entrepreneurial types.
The liveability of cities and their innate urbanity has to go beyond innovative design, or even good transit. Cities need to meet the basic needs of people across income ranges; that is not something one hears talked about much, but it is an essential social role for infrastructure. One sometimes hears the lamentation that places like London and Manhattan are not as interesting as they once were. Maybe that's because no one can afford to live there anymore. I hope Toronto doesn't follow suit in this respect.