The only real metaweb that has worked has been the indirect "share a link" on a link aggregator + comments - exactly what reddit, slashdot, digg, metafilter (funny name huh?) and hn are.
The insight is that there Needs To Be A Central, Browsable Repository of What Pages Have this Meta Content.
Without what is effectively a 21st century web-ring, it's not happening. There should be a page that shows new stuff and a search engine ... I mean essentially reddit + wikipedia. The layer has to a centralized interface
For some websites it actually works quite well. Some users reported it actually "adds a dimension" to the page.
So while i agree universal metaweb is doomed, I do believe in some specific additions from relevant sources.
It also had a central repository of links and users would build "adventures" that were lists of links and you would visit each site along the narrative gaining experience and running into traps laid by other players when you wanted to be active.
I would love to have a layer of academic discourse over anything online, but I agree it seems unlikely this would take off considering how large the world wide web is and how spread out those comments would be.
instead of a central web-ring, what we really need is this standardized meta-layer language over html. a way for people to "write on" a web page, and have it written back to the web server. a protocol that all web browsers speak, and all web servers accept. it could even be more irc like and less reddit like, a live chat that exists between all the people with the page open. it could be both. let clients choose their own way to make sense of the metadata, different browsers can have different comment viewing interfaces and sorting algorithms. i see w3c mentioned, but i havent looked into how it is stored. can a webhost censor comments. is a blockchain between participating servers better, so the data is immutable?
then people can make competing centralized repositories or the pages/servers can communicate with dht/blockchains and create their own decentralized mesh.
Are you able to give further examples of projects like Hypothesis failing? I’m not sure I’m quite ready to conclude this _can’t_ work without a centralized interface.
In any case, though, it would probably be straightforward to add a centralised top stories page while keeping comments inline.
 "Annotating the scholarly web" [ http://www.nature.com/news/annotating-the-scholarly-web-1.18... ]
So if, hypothetically, I ever managed to incite the wrath of an internet mob, they could use this to tack up my family's personal information over my homepage and various profiles, without me being able to do anything about it. Great.
It is clear to me, however, that an annotation layer for the internet is the future. The time to build this is unquestionably now.
That said, I think it would have to be officially recommended by a website before many people would use it.