I'd like social media to be run by everyone having a social media server linked to their home network (imagine something like a Raspberry Pi), with it being totally decentralised and every user controlling their own server.

Then if the government wants to shut it down, they have to raid everyone's home.

Also, what you want already exists - you're free to go use Mastodon and run your own node. You can't possibly think that's a reasonable product your grandparents would be able to use.

BitTorrent certainly isn't illegal in the UK; it might be in other jurisdictions.

> you're free to go use Mastodon and run your own node

Would it work behind a NAT'ed router on a dynamic IP? I suspect it might not.

> You can't possibly think that's a reasonable product your grandparents would be able to use.

What I envisage is an SD card containing the OS + apps, you put it in the Pi, plug it into your router by ethernet, configure it via its web app, and you're ready to go. I think it ought to be possible to make it easy enough for the average person to install (certainly anyone who could install a router + internet would be able to).