[z3t4]

ipv6 solve the problem of one ip per device, with ipv6 you can have both local and public IP's on the same interface! Then your app's and services can choose whether they like to listen on local or public IP's.

Without NAT you can do so much more stuff, like peer-to-peer (p2p) networking. Yes, you can do p2p with ipv4 behind NAT but it's super complicated and brittle.

Also bypassing the NAT is complicated, you have to fiddle with the router settings, and often you have to call your ISP to give you a public IP. This makes it hard or impossible to sell "Internet of things" (IoT) devices to regular people as you can't just plug them in.

Networks today are very good with high bandwidth and low latency, which enables some interesting use cases, for example virtual reality (VR) where you just have a thin client plugged in to the network and then have all the compute power located in a data-center a few miles away, with sub ms latency.

Another usecase is apps with service like functionality, like decentralized Facebook, and chat messengers.