Among 1000's of posts on leetcode, this is by far my favorite post of all time.
I loved the idea of having tweets as linked-list. So, in the db, each tweet will have a link to it's next tweet. And when a tweet is deleted, all it should do is delete that row, and point to next. Also user table having a tweet head link is brilliant idea as well.
The only problem I see here, is that restriction of loading only 10 tweets in timeline. In reality, the user keeps scrolling.
So we should have a feature to get next 10 tweets or something. And this is when we need links to each tweet of her followees that was returned last time.
Now consider cases when tweets keep getting deleted, and we no longer have the chain link. It gets too complicated when all the operations are involved into this.
This is probably why twitter, instagram can get so complicated, and they want smart people to solve big problems.. which is why all of us here are on leetcode. :P