I'm still kinda that Opera Unite didn't take off. It was a decentralized server built into the Opera browser, that was easy enough for regular people to use. You just set it up in a config UI in the browser and could enable features like chat, blogs, photo galleries, a music player, etc. At the time, everyone had UPnP enabled, CGNAT wasn't a thing, and Opera handled UDP hole punching for it, so it mostly just worked. https://www.wired.com/2009/10/opera-unite-puts-the-web-server-in-your-web-browser/

This was back when Opera were still based in Norway, had their own browser engine, and were very innovative. A large number of features that became commonplace were in Opera years before any other browser, like tabbed browsing, full-page zoom (browser zoom used to only increase font size while keeping everything else the same size!), restoring your tabs when you re-open the browser, pop-up blocker, a new tab page that shows your commonly accessed sites, private/incognito browsing, sidebars, and more.

Sure, there's a bunch of downsides to a server being built into your browser, but it was an interesting idea. People that don't know anything about servers were able to easily try it out.

I think that's already a consequence, TCP/IP is very much a protocol suite that works well for client/server architectures, and HTTP (which eventually, somehow, became the de facto "everything" protocol) even more so. So when you mix these roles and you have machines that act as both client and server at the same time all the deficiencies come to light quite easily. A world with first-class support for mutual authentication and authorization, encryption, peering, roaming, etc at the lowest of network levels was possible, but that ship has sailed.