This might deserve an idea of its own, but might there be ways for people to arrange to swap comparable accomodation without significant tax or realtor's fees? (Obviously this would be directed to cases where both parties are able to move closer to their jobs).

Check out "Station C" in Montréal for a very interesting example of a co-working space, of a kind that could be built in suburbs, or in areas where people normally have to engage in long commutes: http://station-c.com/