You could completely eliminate a huge number of round trips by just getting tweet data and user data after the initial pageload. The user data is quite cacheable and you could create a single endpoint that allows the user to precache the required user data (display name, photo url, id, etc) for everyone he follows in one round trip.
They moved away from client-side rendering. Quoting:
There are a variety of options for improving the performance of our JavaScript, but we wanted to do even better. We took the execution of JavaScript completely out of our render path. By rendering our page content on the server and deferring all JavaScript execution until well after that content has been rendered, we’ve dropped the time to first Tweet to one-fifth of what it was.