Pocket would like me to “clarify” that Read Later “still supports Instapaper”, but “discontinued further development”.
My first description, “[Read Later] discontinued its Instapaper support”, was apparently “a shame” to “imply something that isn’t true.”
You can now find Instapaper friends using App.net here http://www.instapaper.com/user/friendfinder (I know, it's ugly, redesign coming soon), or even in the iOS apps' Add Friends pane. (The button says Facebook/Twitter, but it will search here, too.)
Basic Instapaper website support for App.net posting is up. Help me test it by linking your account: http://www.instapaper.com/user
So far, auto-posting Liked items works (even when Liked in the apps), as do the Share links on the Unread page.
I'm adding official support for posting to App.net, and if possible, finding friends and browsing their posted links.
First the Instapaper website, then the app.
(The app will also add "Post with Netbot" to its Share panel.)