As far as I can tell it is basically a CRUD app with some real time analytics to surface some trends.

You said some stuff about Events bubbling, like if I Retweet something you seem to think there's a lot of complexity there. But as far as I can figure all that does is create a new row in a database somewhere and when someone who follows me fetches their feed, my new retweet gets included in there.

Aside from the scale, what's hard about it? Am I completely missing something?