Goal: Create a social-network like UX that gracefully falls back on regular RSS readers, and makes use of all existing RSS feeds.

The latter will allow readers to move to RSSSN and already be able to "follow" a lot of publishers that are not yet on RSSN but only have an RSS feed.

And even publishers who don't have an RSS feed but only a Twitter or Instagram account: Here, wrappers could be written that use the Twitter or Instagram API and create RSS feeds of any account.

So RSSSN is not a website or app or platform but a protocol (superset of RSS) that would allow an ecosystem to grow.

Core ideas

Every account is a RSS-Feed.

Either self-hosted, or on a hosting service: like today a Wordpress blog can be self-hosted on myblog.com or on myblog.wordpress.com. If I move away from myblog.wordpess.com to myblog.com, only my URL changes but the Wordpress UI still remains the same.

Every action (posting, comment, like) is an RSS item.

So both

I ate this soup today!

and a comment to it

That looks delicious. I also ate soup yesterday.

would be separate, regular RSS items from two different RSS feeds:

<item>
<title>I ate soup today</title>
<author>Alice</author>
<guid>id_of_soup_post_from_alice</guid>
<pubDate>Wed, 02 Oct 2002 15:00:00 +0200</pubDate>
</item>

<item>
<title>Comment on post from Alice: That looks delicious. I also...</title>
<rssn:comment-on-guid>id_of_soup_post_from_alice</rssn:comment-on-guid>
<rssn:comment>That looks delicious. I also ate soup yesterday.</rssn:comment>
<author>Bob</author>
<guid>id_of_comment_from_bob/guid>
<pubDate>Wed, 02 Oct 2002 16:00:00 +0200</pubDate>
</item>

So both RSS-items can still be read well with regular RSS readers. And RSSN readers could also read the rssn:… Tags and create a social-network-like UI in their interfaces, i.e. group together post and comment:

Alice: "I ate soup today"

Aggregation of RSS items from feeds I do not follow

What if a reader follows Alice but not Bob – but wants to see all comments to Alice' soup post?

This is of course a feature that regular RSS readers cannot provide. Here aggregation services will help: They are databases that collect GUIDs of posts and comments and likes to them. RSSN readers could send lookup calls for GUIDs to get a list of current comments and likes to a post.