I made something similar last year: A p2p chat popup (that sits on bottom right of the page as a bubble) that allows all visitors to chat with each other. It had simple keyword based moderation in-built (can be easily bypassed though).
Was planning to add github oauth to get a known identity and persistent messaging so visitors can chat with each other across sites.
Instead of a webmaster adding script to their site, it was a browser extension.
The intent was two folds:
1. Get to know other people having similar interests,
2. Try something on the lines of a decentralized chat/messaging system.
It sounds like a nice idea, but probably only one of those things that work only once at scale - with hundreds of millions of pages, you will only meet others on the most common ones unless the extension is already very popular?
That's true.
Site-local chat was meant to be the default way. But, was not restricted to that. People could keep whitelisted list of sites that they are open to get pings/DM's from.
I was still not able to figure out the privacy-focused, and local, interest matching part since it was meant to be p2p (without any server storage), and local storage can easily be tweaked.
If this was solved, my plan then was to automatically suggest people who may have similar interests depending on the sites they browse, for how long, and the messages they generally send.
Kinda like tinder, but, you don't have to sign-up and install no app.
The network effect is HARD