I think the writing is on the wall for Twitter. The younger generations are increasingly flocking to snapchat, yik yak, and similar apps. I never hear of anyone using it anymore(college student here). I would have stopped facebook a while back as well if I didn't use OAuth for damn near everything
Snapchat and Yik Yak are messaging applications, so they attract kids and friends who want to communicate with one another privately. Problem is, messaging apps don't seem to be revenue generators anymore.
Because Tweets are all public and searchable, I would argue that Twitter is a publishing platform. They attract content producers who want public attention: press, celebrities, politicians, brands, etc.--and the audiences who want to hear from these folks. So they should be able to drive a lot of revenue from ads.