For buildings that are partially built, can they still be converted or is it too late?
https://www.nytimes.com/interactive/2023/03/11/upshot/office... https://archive.is/gQiQW
Floor plans are awkward if you had to segment them in to apartments, having each apartment meet code for residential spaces turns in to a puzzle in ensuring things like light entry. Math that made sense for office buildings doesn't translate as easily to residential, so you're paying for more elevators (made for an office building) than you need, you have less floor space you can rent out because you need it for amenities, you have to do extensive renovations to make it suitable for living, and then have to hope the commercial real estate market doesn't surge in demand after you've done it.
It's apparently doable, but not easy, and has a significant downside if there isn't enough demand to meet your new luxury apartment building, and the risk that commercial real estate bounces back after you've done it.
There are other factors, too, but the plumbing seems to be the biggest hurdle.
For the most part, there are no insurmountable engineering issues. It's just a question of cost.