The plot twist in this system is blocking, muting, and locked accounts, which make denormalized timelines a lot harder. You basically need a very fast side syst

The plot twist in this system is blocking, muting, and locked accounts, which make denormalized timelines a lot harder. You basically need a very fast side system that can be queried for visibility, especially because eventually consistent privacy features (i.e., running a "account became locked" feature on a similar queue to "fan out tweets" in your model) are not treated lightly by customers.