Even setting aside the UX issues in this, I think this is underestimating the complexity. I don't know anything about Twitters infrastructure but obviously we a

Even setting aside the UX issues in this, I think this is underestimating the complexity. I don't know anything about Twitters infrastructure but obviously we are not talking about a single postgres instance here. Effectively turning every tweet into a linked list with connected retweets, likes etc. is a significant data model change for a system of this scale.