Cycling?

As I was walking the dog this morning, I saw a few houses with additions under construction. That got me thinking about how house size seems to go up and down. Houses in the US used to be pretty small. Then back in the early 1900's some people built really big houses By the 60's, many of them were split up into apartments because they were too big for a single family to afford. Lately, we've been having McMansions and people wanting a large house. How soon before we have another cycle where those big houses are converted into multiple family dwellings because they aren't affordable?