It's not a bad way of building in all seriousness. A lot of these buildings have a lot of embodied energy in their development so preserving the shell like we see here is a sustainable choice for intensification.
I'm still not happy that Lanterra/P+S couldn't have found a way to preserve the Brutalist/International Style facade of the Sutton Place for the redevelopment, but it is interesting watching this morph at the moment.