There was an effort many years ago to provide browser extensions that allowed users to mark up, edit, and annotate existing web pages in a way that would be visible to the community of users. It never went anywhere, unfortunately, probably because it would have gored way too many sacred oxen. (And/or it would have been co-opted by spammers, turning it into a social networking/reputation management project.)
Every so often someone announces that they've reinvented that idea but it doesn't go anywhere. These days the problem is probably mostly mobile Internet, but also the sheer difficulty bootstrapping enough of a community for it to be worthwhile.
And of course any such project that became popular would either ruin the creators as they try to keep up with moderation, or devolve into an unusable mess if they don't moderate.
There was an effort many years ago to provide browser extensions that allowed users to mark up, edit, and annotate existing web pages in a way that would be visible to the community of users. It never went anywhere, unfortunately, probably because it would have gored way too many sacred oxen. (And/or it would have been co-opted by spammers, turning it into a social networking/reputation management project.)