I don't think you can call it a fad because that implies that it's a purely social phenomenon, but in reality it appears to be tightly intertwined with economic

I don't think you can call it a fad because that implies that it's a purely social phenomenon, but in reality it appears to be tightly intertwined with economic factors. In particular, it seems to be mostly financial issues that are encouraging the shift in the US towards multi-generational households.