Have you heard of [syncthing](https://syncthing.net/) ? It syncs a folder between devices, like Dropbox, without the need for someone else's computer. No cloud, it's just your pc talking to your phone, directly and automatically, through your home WiFi.
Have you heard of yggdrasil?
I was trying to find a summary of what it does, but couldn’t. That’s how far I’ve got.
https://yggdrasil-network.github.io/
sorry for not providing a link. It’s not totally related to legacy ip, but might be interesting in the context of the whole topic.
tldr: it’s an encrypted mesh network on top of the internet (and every member gets an yggrasil ipv6 address)
Yes, that seems all like neat technology, but what is the use-case for that?