> and later when serving each follower's timeline, fetch the celebrity's posts and merge them into the timeline

I think then you still have the 'weird user who follows hundreds of thousands of people' problem, just at read time instead of write time. It's unclear that this is _better_, though, yeah, caching might help. But if you follow every celeb on Bluesky (and I guarantee you this user exists) you'd be looking at fetching and merging _thousands_ of timelines (again, I suppose you could just throw up your hands and say "not doing that", and just skip most or all of the celebs for problem users).

Given the nature of the service, making read predictably cheap and writes potentially expensive (which seems to be the way they've gone) seems like a defensible practice.

> I suppose you could just throw up your hands and say "not doing that", and just skip most or all of the celebs for problem users

Random sampling? It's not as though the user needs thousands of posts returned for a single fetch. Scrolling down and seeing some stuff that's not in chronological order seems like an acceptable tradeoff.

You might mix the approaches based on some cut off point