The borough of Manhattan seems to be prominent in skyscrapers and towers that seemed to endlessly reach out for the heavens. However, the lesser boroughs of Brooklyn, Queens, and Staten Island seemed to not be as densely populated and skyscraper-filled as Manhattan. Staten Island, in particular, seems underwhelming.
How can the lesser boroughs become more densely populated ? How can Brooklyn and Staten Island increase its skyline ?
Kill the interstate system. There will be "White Flight," but it won't be to Westchester and Putnam County if they cannot easily travel there. The neighborhoods would just get more gentrified.
Also, you need to kill rent control, so that the landlords could make money having housing and not let it all burn down, or like my grandfather did with property in Soho (!) as well as the Bronx, just stop paying taxes on it and abandon it.
Also, if NYC bucks the trend of industrial cities and does not tax everyone to death, you can keep more of the urban workbase (though not indefinitely obviously, but long enough to change the demographics of NY.)
Also, kill the Warren supreme court and get rid of bussing, so that schools will accurately represent the socieoeconmic make up of their neighborhoods, which will keep much of the NYC population from moving into Long Island, Jersey, Westchester, Rockland, Putnam, etc.
If all of these things happen (which may require a pre-ww2 POD, like a communist Hitler or something to change NY politics) then NYC will be way more dense.
I grew up in a suburb where EVERYONE is from the Bronx. I have only found out as an adult that the way I talk is a Bronx accent (I was always under the impression that all NYers spoke that way as the suburbs are all Bronx transplants north of NYC.) All the stuff I listed was the reason why EVERYONE left the old neighborhood. And, we are talking about a bunch of Italians and Irish...they LIKED the old neighborhood until it was not THEIRS anymore.
So, the cost of making NYC more dense is to set back race relations a few decades, sorry to say.
Do not take this post as an endorsement of any policy of making NYC more dense.