Really interesting project. I’ve never worked on my linked profile because I dont think a 3rd party should be the custodian of your working profile
Linked data (the LD part of JSON-LD) is perfectly designed to create profile data in an extensible way.
In fact as far back as 2004 the FOAF network was gaining traction, but it never made it to mainstream, tho at one point in time google did say they were going to implement it. That sadly didnt happen.
Creating a profile is not too hard IMHO. You just extend the JSON (LD) to add the fields you want. Annotations should not be too hard either, you just add extra objects linked from that profile. LD is designed specifically to do that. I’ve read some understandable criticism of JSON vs JSON-LD but this is the use case the LD part was designed for, so if AP is embracing LD there might as well be some benefits!
Relationships between profiles. This is what we used to call the “social graph” back in about 2006. Another great idea which unfortunately didnt take off yet. During the social web working group where AP was developed I argued that the social web was about people, friends and relationships. Something that I considered self evident at the time. To my slight surprise I was almost the only member of the group that had this mind set. The over riding wish was to build out the open microblogging specification which was based on tweets and followers. The message was, “not now” for friending and social networks. Let’s get the micro blogging done then look at other things. There was also a degree to which some folks thought that reciprocal following was like friending.
Linked data is designed through the use of "ontologies’ to give all sorts of different relationships. The most common being foaf:knows, but the idea is just come up with a URI and that describes the TYPE of relationship.
Regarding identifiers. The Solid Project (social linked data) was designed along these lines with friends and profiles in a social graph. In that case the user is identified by their profile URL. In mastodon it uses the @ syntax. I’d like to actually maybe code a server that does both and brings the two projects closer together. It’s possible to put your profile data in a script tag in your page, which is the idea I would like to personally explore.
Regarding privacy, in solid we have a notion of access control. It’s quite complex, so maybe the notion of public/private/local would be a simpler way to go.
Great idea, looking forward to what you come up with!