I get @TomCritchlow’s sentiment, but… the extra “work” it currently entails for the social part dramatically ups the signal to noise ratio for me compared to Twitter.
You’d definitely want the ability to filter by your social circle, especially on popular sites. In fact this sort of discovery mechanism would be cool if it could be more broadly built into either the web or perhaps into IndieWeb social readers which would know your social graph and could surface related details.
Perhaps expanding a browser extension like Crowdwise to include Twitter support might be a potential solution? I would worry that portions wouldn’t add much other than a lot of likes and bookmark-like data. While some,  might consider Twitter as an annotation layer (not always directly linked) on the web, the overall quality isn’t necessarily going to be built in there.
It would be cool if Crowdwise also added Hypothes.is’ API to their list of sources.
I’m also reminded of Peter Hagen’s experiments with Hypothes.is seem very similar but with a different UI. His version flips the discovery question on its head.
Piotr Wozniak has some material on creating/designing more concrete cards for spaced repetition that I’ve found generally helpful. I know that Andy Matuschak and Soren Bjornstad have some ideas, experience, and research in the space but I’ve yet to see more deep research on the effectiveness of these more specific practices at scale or beyond the anecdotal.
Alberto Cevolini & Markus Krajewski have relevant research. There are still a few missing puzzle pieces however.
I’m always curious to see other implementations.
Your challenge question is tough, not just for the mere discovery portion, but for the multiple other functions involved, particularly a “submit/reply” portion and a separate “I want to subscribe to something for future updates”.
I can’t think of any sites that do both of these functionalities at the same time. They’re almost always a two step process, and quite often, after the submission part, few people ever revisit the original challenge to see further updates and follow along. The lack of an easy subscribe function is the downfall of the second part. A system that allowed one to do both a cross-site submit/subscribe simultaneously would be ideal UI, but that seems a harder problem, especially as subscribe isn’t well implemented in IndieWeb spaces with a one click and done set up.
Silo based spaces where you’re subscribed to the people who might also participate might drip feed you some responses, but I don’t think that even micro.blog has something that you could use to follow the daily photo challenges by does it?
https://daily.ds106.us/ is a good example of a sort of /planet that does regular challenges and has a back end that aggregates responses (usually from Twitter). I imagine that people are subscribed to the main feed of the daily challenges, but I don’t imagine that many are subscribed to the comments feed (is there even one?)
Maxwell’s Sith Lord Challenge is one of the few I’ve seen in the personal site space that has aggregated responses. I don’t think it has an easy way to subscribe to the responses though an h-feed of responses on the page might work in a reader? Maybe he’s got some thoughts about how this worked out?
Ongoing challenges, like a 30 day photography challenge for example, are even harder because they’re an ongoing one that either requires a central repository to collect, curate, and display them (indieweb.xyz, or a similar planet) or require something that can collect one or more of a variety of submitted feeds and then display them or allow a feed(s) of them. I’ve seen something like this before with http://connectedcourses.net/ in the education space using RSS, but it took some time to not only set it up but to get people’s sites to work with it. (It was manual and it definitely hurt as I recall.)
I don’t think of it as a challenge, but I often submit to the IndieWeb sub on indieweb.xyz and I’m also subscribed to its output as well. In this case it works as an example since this is one of its primary functions. It’s not framed as a challenge, though it certainly could be. Here one could suggest that participants tag their posts with a particular hashtag for tracking, but in IndieWeb space they’d be “tagging” their posts with the planet’s particular post URL and either manually or automatically pinging the Webmention endpoint.
Another option that could help implement some fun in the system is to salmention all the prior submissions on each submission as an update mechanism, but one would need to have a way to unsubscribe to this as it could be(come) a spam vector.
Most often we privilege the chronological time order because that’s how we ourselves live them, write them, and how much of our audience experiences them.
But consider looking at someone’s note collections or zettelkasten after they’re gone? One wouldn’t necessarily read them in physical order or even attempt to recreate them into time-based order. Instead they’d find an interesting topical heading, delve in and start following links around.
I’ve been thinking about this idea of “card index (or zettelkasten) as autobiography” for a bit now, though I’m yet to come to any final conclusions. (References and examples see also: https://hypothes.is/users/chrisaldrich?q=%22card+index+as+autobiography%22).
I’ve also been looking at Walter Benjamin’s Arcades Project which is based on a chunk of his (unfinished) zettelkasten notes which editors have gone through and published as books. There were many paths an editor could have taken to write such a book, and many of them that Benjamin himself may not have taken, but there it is at the end of the day, a book ostensibly similar to what Benjamin would have written because there it is in his own writing in his card index.
After his death, editors excerpted 330 index cards of Roland Barthes’ collection of 12,000+ about his reactions to the passing of his mother and published them in book form as a perceived “diary”. What if someone were to do this with your Tweets or status updates after your death?
Does this perspective change your ideas on time ordering, taxonomies, etc. and how people will think about what we wrote?
I’ll come back perhaps after I’ve read Barthes’ The Death of the Author…
Also in reply to:
If it’s your dream, I hope you look into the solutions and come join the growing community.
Mae’r Gymraeg yn fy ngwneud i’n hapus.
You’d probably also really enjoy Japanese onomatopoeia.