This is @deoxxa's overview of the various components of OStatus: https://www.fknsrs.biz/blog/don-statusnet-node-part-one-read-protocols.html

It's worth reading. IMO the component to think about is PubSubHubbub. Specifically, the hubs, which serve as notification intermediaries between publishers and subscribers.

Key notes:

1. Hubs do NOT need to be Twitter-like user homes.
2. Hubs are very capable of tracking user behavior, even if notifications are encrypted.
3. Hubs need to be reliable.

So the question: how to make hubs that are/have

* reliable
* trustworthy
* non-exploitative of users
* non-authoritarian (wrt censorship)
* proxy-able
* graceful failover
* graceful obsolescence
* potentially anonymous
* potentially transient

I think in the absence of these considerations, mastodon networks will, as others like @bcrypt have pointed out, tend to consolidate around a few large instances that will have too much trust & reliability burden placed on them.

@bcrypt @auerbach ping me with an email address if you want an invite to a brainstorming doc around community functionality.