Yes, this is a great idea. This would have been built a long time ago, however zoning doesn't allow for it in the vast majority of cities in the US. California

Yes, this is a great idea. This would have been built a long time ago, however zoning doesn't allow for it in the vast majority of cities in the US. California is making a tiny bit of progress by pushing for ADU's, but for the most part, it's just not allowed.