For example, many of their users are quite passive - why not improve the experience for the logged-out user? Twitter could be a great source of real-time news for everyone - not just heavy users of the platform.
In addition, did you know that if you paste a url into the search you can see the tweets that link to it? There are great conversations happening about published stories - yet that content has no way to get surfaced, really. I should be able to see the twitter conversations that are happening around every piece of content on the web, and I can't! That's crazy.
I get that design is important, but Twitter needs to innovate on its product. Rant over.