There might be no fixing Twitter. The reason Twitter grew imho is because of the rich ecosystem of developers they had. Those developers, time and time again, found new ways to use Twitter and did the development, marketing, and educating of the public. The result was rich engagement and growth.
Everyone had a different reason for using Twitter because there were so many apps. Now, those apps are gone. How do you go and tell the developer community to come back? How do you trust Twitter? The answer is you don't.
Indeed. The trust has been lost. Trust is a really simple issue that many people in our industry like the article's author simply don't get. To expect Twitter to recover in this area is absolutely ridiculous. Yes, there are plenty of young, stupid developers, but given Twitter's animosity towards developers in the past, even with a dedicated campaign, I doubt they could get any significant ones to work with the platform again. From a business' point of view, it's suicide, from a developer's point of view, it's a waste of time and effort, and from an investor's point of view, it's a risk not worth taking.
I can believe that the growth was significantly helped by third-party clients, but I wouldn't believe that the more creative twitter integrations had a major effect. That would be a dev/techy-centric view of the world, similar to those that truly believe that the real-name policy was a mainstream issue that killed G+.
When I started on twitter, it had no hashtags, replies were public (because they weren't initially part of the protocol), no t.co, no embedded photo sharing, no geotagging. All of these features were added, and made popular, in third party clients before being added to Twitter. It was like a giant lab where the features could be tried by smaller groups who shared certain clients or norms and the popular ones wrapped into the "official" API eventually.
Everyone had a different reason for using Twitter because there were so many apps. Now, those apps are gone. How do you go and tell the developer community to come back? How do you trust Twitter? The answer is you don't.