[lostmsu]

I was not proficient enough to understand that on my own. ELI5 is that this requirement forces apps to support running on IPv6-only networks where DNS calls return special IPv6 addresses for IPv4 hosts and ISP (usually mobile) does IPv6 to IPv4 NAT. That does sound useful.

[WorldMaker]

Right. It's useful to point out too that for some of our day-to-day mobile networks this is the present state and not just a hypothetical future. Mobile and cell networks have been a driving force for IPv6 adoption [1] and several of them went IPv6-only infrastructure years ago (hand in hand with 5G rollouts in many cases). Both iOS and Androids efforts in making sure that IPv6-only was standard and worked in all App Store/Play Store apps were critical to getting us here.

[1] IPv6 makes hand-offs between radio towers (cells) a lot easier if the towers don't also have to manage scarce IPv4 addresses/NAT44 configurations and complicated DHCPv4 handshakes to setup/change IP addresses regularly; plus mobile networks in general have a lot of devices today, some have way more than other types of ISPs so IPv4 scarcity was something they could feel directly on their corporate bottom lines.