Annotation is now a web standard

"Arguably we still do not have a satisfactory realization of the memex."

Yup.

A related issue: Ted Nelson's original idea for hyperlinks had them working both ways. When one document linked to a second document, the second document would automatically get a link back to the first. His idea also had what he called "transclusion" -- sort of like block-quoting someone else's text, but with the feature that when the quoted text was updated, any document which had transcluded it would also automatically get updated.

Of course, there are some practical issues there, not the least of which is (as several others have mentioned) vulnerability to spam.

Where will be the annotation data stored?

Federated comments/annotations sound really cool from a developer's point of view, but also seem like a nightmare for publishers. If you cede administrative control over the comments on your site, how do you control trolls/attacks/spam/etc.?

Services like hypothes.is can do some filtering automatically, but this is missing the level above that - editorial privileges on comments on your own domain.

The annotation system of the web is reddit.

I profess I don't know much about the company, but this effort is a continuation or an application of the W3C Linked Data Platform [1] initiative that are attempts to put Tim Berners-Lee's ideas [2] about the Semantic Web into practice, with renewed vigor and buy-in from many interested parties, and not speccing for its own sake.

Adoption is always the question that matters most to the public; arguably TBL's mid-2000s vision for the web as a Giant Global Graph [3] has been neatly cloned and co-opted by Facebook's concrete, incompatible, and inward-flowing Hotel California implementation [4], but if a new wave of startups and bigcorps can create a rich ecosystem using community-designed standards, the outcome may be different this time. Or maybe not, but I applaud and support them in trying, and I will evangelize the same.

What's different from the mid-2000s, you ask? For one, the ideas behind REST, despite often imperfectly or incompletely applied, have nonetheless entered community consciousness. Hard-fail-if-invalid attitudes have been replaced by a tolerance for imperfections, both in the community's rejection of XML-derived data formats, and an acceptance of the web's often haphazard, something-is-better-than-nothing nature. APIs implemented using HTTP over the Web are a mainstay instead of experimental integratons, and a new wave of commercial players is eager to exploit whatever competitive advantage against the incumbents.

The big content gardens have all pushed incompatible "protocols" (we call them APIs, but they behave like protocols) [5], which gives them network effects but also locks them (deliberately) out of the open web (i.e. a Facebook comment on a Facebook post that was spawned by sharing a web link is not a comment on the link; it's a comment on that Facebook post). Meanwhile, systems that can build on top of these standards to implement two-way data flow -- both inward and out -- can present richer experiences, while not precluding the usual business models and monetization schemes that are in use today. And even if commercially this all flops, we'll have nice specs and vocabularies to use where metadata is paramount: science, research, government, and the like.

[1] https://www.w3.org/TR/ldp/ [2] https://www.w3.org/DesignIssues/LinkedData.html [3] http://dig.csail.mit.edu/breadcrumbs/node/215 [4] https://developers.facebook.com/docs/graph-api/overview/ [5] https://news.ycombinator.com/item?id=12893852