In 2016, I was at a real estate innovation conference and one of the top awards went to the Next Gen home by Lennar, one of America's biggest single family homebuilders. It was popular with immigrant families, who, like you write, fit several generations in one household. That possibility is there for non-immigrants as well, and the poorer ones do that; the government term for this is "doubling up," not community. That said, creative reuse of a bad design does not make it ideal, and the car and sprawl issues are still there even when housing density go up.
I bought a home with my ex wife a little over a decade (I'll link to a story about it below). It was a huge stretch, and tons of things had to go right to make it happen (including, full disclosure, family and sponsor assistance). I would not be able to do it, nor would I do it today.
