I don't know anything about renting/buying/homeownership in South Korea but to me it seems like you could still have people living in these basements if you could ensure they don't flood above head-level with sump pumps or building a dike around the building or something? Not sure. Seems like it would be a good stopgap solution while still making sure tenants don't get their lives upended by flooding or laws that force them out of their homes.

It's funny because we've been starting to see homeowners of larger houses where I live renovating their basement into a condo/shared living space of sorts then renting it out to younger generations of people who can't afford regular apartments or housing.

I'm fairly certain we're going to see an economic collapse on a larger global scale in the next decade and some governments' complacency on housing availability/affordability/etc. are going to be part of the blame.