I saw the thread title and immediately thought of stacked shipping container homes, Kowloon Walled City, and futuristic dystopian slums. That took me down a rabbit hole that lasted nearly an hour. Did you know that Kowloon Walled City had a population of somewhere in the neighborhood of 2 million people per square kilometer at its peak?
The idea would be to have multi-family units of 1800-3000 square feet on top of each other, priced above condos but less than houses.
As for this... given the competition for housing, it seems unlikely that these would stay affordable for long, even if they were intended that way.
-k