Plastics were off to a rocky start, but are much improved now no?
Hell no.
What has eluded me so far - perhaps one of the proponents of massively overhauling the U.S. infrastructure can speak to this?
Question 1:
What would the U.S. look like with an optimal infrastructure? i.e. what would the population density be? What would the typical housing look like for everyone?
Question 2:
What would the timeline be assuming everything comes up roses, everyone votes to support this, every politician finds the money to incentivize the changes?
If anyone would be able to answer that with certainty, that person would a jackpot lottery winner every few weeks.
The time frame is the easiest question: About 20 years, if you really want. 20-30 years is how long it takes to rebuild a completely war-destroyed country.
Of course it would not be perfect - it would be bloody stupid to destroy good houses build today just because they are not perfect - but close enough. Incidentally, that is roughly how long we have if we want to prevent literally billions of people losing their home to climate change.
Question 1: Anything made on this topic is a lot speculations. And they will be wrong. That is because we have an understandable problem imagining what we have never seen before.
If you would have asked people 50 years ago about the most used method to talk to someone far away, they would have probably said TV-phones. They would have said that we will be able to talk to everyone from everywhere, while having a picture of them (in color!) at the same time.
And that is more or less true. But they would have imagined a literal TV (not a flatscreen btw.). Not that tiny technological wonder we know as smartphone, and having the ability to have those TV-talks is just a tiny, tiny and practically unimportant thing compared with all the other stuff it and the internet allows.
As far as housing goes, traditional single family houses will hopefully be out of demand, since they cost the money they really cost. Maybe earthship-like buildings will be used by those who really want that loner life.
Apart from that, density is not a usable measurement of living conditions or style. Example: How many parks will be there to dampen the effects of climate change?
What is quite sure is that some sort of multi-generation living will be more widespread. That is a trend that is already happening. Even if they are not blood-related, young and old will be living closer to each other in arrangements of e.g. "I go shopping for you, you watch out for my kids".
A VERY big part will be decided by the way we treat climate refugees. Will we welcome and integrate them? Or will we put up fully automated borders with KI controlled guns shooting automatically at the millions of people that will come every year? Will the xenophobic, control-obsessed people force a police state on us?