In a surprise to no one, developers of these apps have been left in the dark, as The Iconfactory points out in a blog post:
There’s been no official word from Twitter about what’s going on, but that’s unsurprising since the new owner eliminated the employees dedicated to keeping the API up and running smoothly, including the developer evangelists who previously provided communication with third-parties.
We wouldn’t know whom to reach out to at Twitter even if such people existed. We’re in the dark just as much as you are, sadly.
As soon as we have a better understanding of what has happened, we’ll update this blog post and let you know. In the meantime, if you own a Mac you can use Twitterrific for macOS (but we don’t know how much longer this will last).
January 14 Update: Twitter hasn’t announced anything, but it looks like this is indeed intentional.