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?
Because the client-server paradigm means than an instance can’t be hosted by a mobile client (and even if it could, the system relying on DNS or a static IP wouldn’t work as most mobile IPs are dynamic) and thus should be provided by someone at a loss (or other user-hostile business model such as advertising if not outright extortion). The system needs to be as easy as Facebook/Instagram/Twitter if it wants to succeed. Having to manage a domain or a (stateful) server is a non-starter.
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.
This doesn't make much sense. I agree: the instance won't be mobile. It'll be hosted, the same way Blogger was. It'll be provided with the same economics as Blogger. Manage a domain? Most people will be "theirdumbname.mastohost.com". For like 20 different values of "mastohost". Those "mastohost.coms" will make all their money on the subset of people who will provide a credit card to be "theirdumbname.com".
People are sleeping on how well the blogosphere worked, and how much Twitter and Facebook were able to divert it purely through a catchy UX. The blogosphere now has that UX: it's called Mastodon. Meanwhile, Twitter and Facebook are collapsing, because the centralized social network is inherently unstable and susceptible to gaming.
