to give you an example: in case of email, though it is not that difficult to host your own server (and even if you are a small startup you'll most probably do so without much effort), in the end basically Google decides on "who is an accepted participant in the network". If Google deems you spam, you are spam. If Google deems your authentication emails "promotion", for most intents and purposes, you are "promotion" and your users will miss your emails.
that, I feel, is an inherent limitation of any federated system, specifically one whose design is really inspired by email.
> I don't see how that follows.
as you've mentioned right after.
> work is better distributed temporally (since consumers hopefully poll the feed in a randomized way independent of new posts appearing).