I'm uncomfortable with hub-runners deciding which other instances they do and do not federate with. People can certainly run filtering services, but they should be independent of instances/hubs, not tied to them.
For similar reasons, I don't think hubs/instances should be thought of as communities with individual cultures, because you then turn the hub-runner into the de facto community leader.
Running a SMTP/NNTP/OSocial server shouldn't make you a doyenne. People get high off of that power.
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.
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.
TheShadowBrokers to Trump:
"You not being in office three months and already you looking like the MIIC’s bitch with John McCain and Chuck Schumer double dutch ruddering each other in the corner over dead corpses.
"Your Supporters:
- Don’t care if you swapped wives with Mr Putin, double down on it, “Putin is not just my firend he is my BFF”.
"Therefore Russia and Putin are being best allies until the common enemies are defeated and America is great again."
Looking through the code and, in particular, at the targets I am surprised that there appears to be nothing for either VMS or NSK (Tandem) both of which used to run the vast majority of telcos in the 90s.
I assume the targets, being mainly "non-aligned countries" (to use an old name), might have used cheaper technology but I am pretty confident some of those (e.g. Taiwan) would have used the "Western standard tech".