There is a great use-case for IPV6 for IOT where each device gets its own IPV6 address. IPV6 addresses are appearing more like MAC addresses at this rate as IPV6 is not exhausted yet.
The world will be a completely unrecognizable place when this is even a slight concern.
But seriously, there's an astronomical # of addresses in IPv6. You're probably right that if we ever exhaust that space, we'll probably be communicating between planets by then.
And they were right!
Do you really want your IOT devices to be directly addressable on the internet? It's my understanding that having devices behind a router is safer. I go a step further and disable UPnP on my routers and everything still 'just works' including network printing.
I have a gigabit fiber (to the home) connection which terminates at a device with 4 Ethernet jacks. They all work, I've tested connecting directly to them with a laptop, but I plug a router into it and all devices connect through that router instead. It's the 'stateful firewall' aspect of using a router that I want for improved security. https://en.wikipedia.org/wiki/Stateful_firewall
You supposed to control access with firewall, and controlling security is much easier when computer/device has a routable address.
Though, IoT devices should probably be restricted of any Internet access based on their security track record (but again, this is orthogonal to being directly addressable).
I still don't see a reason for the average consumer to have a static, reachable IP for their devices. I see privacy concerns but no advantages.