I heard a developer speaking today, and he said that he is making a presentation to Public Housing Qld in a few weeks, and he will be suggesting building smaller, higher density, units to solve their problems.
He was also talking about subdividable homes - so houses built in such a way that they could be easily partitioned off in the future to subdivide into a duplex - this would require the additional of wet areas (kitchen, bathroom, laundry) to the second unit, but if the house was designed with this future application, then it would be easily modified.
This would mean that a family could live in a house, then once the children grew up and left home, the house could be divided with the couple staying in part of their exisiting home, with the other part becoming a completely self-contained unit. Thus tenants wouldn't need to move, nor would they be sharing. They would be able to downside in the same house.