This is not a new practice. In many regions across the world, families have comfortably lived in one house for generations. Also auxiliary apartments within units are very common in most countries and provide for viable alternatives to increase the efficient utilization of the residential area. Increase density housing in Boulder, Colorado. Solar response units along river-greenway park.
Density naturally increases adjacent to urban amenities.
B.C. Historic units are subdivided into apartments and the space in the back is used for new infill multi-story apartments.