Literally all of those are solved problems.
The reason you can't connect directly to other hosts has more to do with firewalling than NAT. Piercing NAT from inside a firewall is a solved problem. BitTorrent proved that decades ago.
Their are a dozen P2P file sharing networks and P2P Facebook knock-offs. Several of them make onboarding new users pretty painless. They have failed to set the world not for technical reasons, but for humans ones.
Facebook and google have market share, mind share, and user inertia. Even a free, easy to use service that is BETTER will fail unless it can outspend both of them. An added issue it that without the (Hard, expensive, intractable) problem of content moderation solved, any free or egalitarian p2p network gets blitzed by terrorists, hate groups and spammers.
Once they set up shop, no one else want's to hang out there anymore.
But even if you sort those issues out, you're still gonna get Zucked and run into the ground by a couple billion $ signs.
Biting the hand that feeds IT
