@evan

Ideally —

...

For the former —

From a UX point of view, they (Bob's followers who don't yet follow Alice) could see a placeholder post for Alice's post(s), that says that the content cannot be shown.

If a follower of Bob's then followed Alice, then the placeholder post(s) would turn into the actual post(s).

...

For the latter —

Again, from a UX point of view — Placeholder posts, until they follow Alice or Bob.

.

@reiver so, like sitting in a room with someone while they talk on the phone, and you only hear their side of the conversation.