I think of kowloon as a preview to the hyperdense cities of the future in a way.
Acrologies would be a more workable vision of hyperdense cities, as you also need green spaces rather than just a bigger version of dense concrete jungles that is defacto state of many cities.
Right now, space is criminally underused in cities or allocated so inefficiently that we don't really need acrologies yet. We can get more green in cities and making these places more pleasant and human space to live.
"Dense" cities are necessary for achieving the efficiencies of density, but "hyperdense" cities are not. You can have a city where all residential buildings are five- to six-stories, with ample green spaces and every street lined with trees; that would be a dense city, despite being less dense than Manhattan.
I don't foresee a future where any city feels the desire to model itself after the Kowloon Walled City in terms of density, because in order for that to happen it would have to imply that physical space itself is the bottleneck for the population, rather than things like the availability of energy/food/water (which was true for the KWC for historical/political reasons).
Note that the walled city is just a small part of Kowloon district. The famous Kai Tak Airport was also in Kowloon (now converted into an event space), where airliners flew scarily close to buildings on final approach.
I lived in Hong Kong just under 10 years, and a friend of a friend grew up in the walled city.
According to Wikipedia, China actually handed over sovereignty of Kowloon to the British to facilitate demolishing it. They must have really hated the place.
The more interesting question is why so many people feel this place in the first place. Why this puzzling fascination? I don't have this with any other place.
Why do the pictures feel like home?
While I shouldn't, I remember it as people struggling to make ends meet but also as an incredibly happy place because of the tightly knitted social fabric. The need to help others and the need to be helped creates top notch relationships.
Right now, space is criminally underused in cities or allocated so inefficiently that we don't really need acrologies yet. We can get more green in cities and making these places more pleasant and human space to live.