Earlier quoted context omitted.
But the concept of instances raises a lot of issues as I’ve described. Google Reader/RSS works for its purposes because there is no instances and most of the work is delegated to the client.
And why won't that be the configuration ActivityPub converges to? Why will people be signing up for random group instances rather than just pushing a button to get their own? That's what happened with blogs. Why won't it happen here?
RSS doesn’t have this problem because it doesn’t require the client to have a static hostname, thus mobile RSS clients are totally possible.