I mean it's probably crazy to imagine a scenario where we have more than 4 billion "local internet registries" in the universe, but it's not so crazy to imagine a scenario where the ability to ask for a /32 maybe needs to get constrained a little more.
In the end, I think the idea of making all subnets /64's may have been a mistake. It's cool that you can put MAC addresses right in the address and thus don't need DHCP any more, but carving out room for 18,446,744,073,709,551,616 devices per broadcast domain is a bit crazy on the face of it. Plus you need all the privacy addresses to hide your MAC address from trackers anyway, which is way more complexity than we really needed. IMO DHCP isn't so bad, it's boring/predictable technology at this point, and I'd be perfectly comfortable with shifting the "provider vs customer" boundary many bits to the right in an address, so that a typical subnet is more like a /104 and ISP's give out /96's, etc. That would give us a lot more headroom than the system we have now where anyone can grab a /32.