In the US for home connections (cable, fiber, DSL) everybody gets an accessible IP address pretty much -- the worst is that some ports are blocked like port 80 or 25. Phones don't get a dedicated IPv4.
In other parts of the World that didn't get as many IPv4 addresses as the US, the standard for home connections is that you DON'T get a public IP address, you get a private IP address behind carrier grade NAT
And that's really NAT, not a firewall, so nothing is "blocked".
You do get public IPv6 addresses from some ISPs, though.
I have a rpi set up with a minutely cron job to update my domain name to point to home. Works pretty well. At the worst you lose connection for a minute but usually the IP address only changes when the home connection fails which can take more than a minute to reset anyway.
Why not? It is pretty simple and very fun! My first project in golang was a program that polled for the machine's IP address and updated a AWS Route53 record.
Its not exactly "write your own" I have a single line in my crontab that just uses curl to post to a url and the remote server takes the IP address it got the request from and sets the dns to that.
Though usually on firmware like openwrt the request going out is tied to a particular interface going up (and down) as it should be, so its somewhat more robust and 'correct' than crontab would be.
Dynamic in theory, but for many people the IP is unchanged for a long time. I remember reading an article that said the average length of time between dynamic IP changes tracked by some company was something like seven months, though I can't find it now.
I have cable with a theoretically dynamic DNS but it's changed once in >4 years.
And that's really NAT, not a firewall, so nothing is "blocked".
You do get public IPv6 addresses from some ISPs, though.