It’s not even clear that they “pulled the plug”, could just be a temporary outage. Wish Musk would announce his thoughts on the future of the API, though.
Regardless of how it started, a "temporary outage" that has lasted for several days and has received zero acknowledgement from the company can now be considered intentional. They don't get the benefit of doubt without sending even a bare minimum "sorry, we are working on fixing it" tweet.
Can a “temporary outage” be limited only to the most popular apps? Can a “temporary outage” affect Twitterrific for iOS but not Twitterrific for Mac [0]?
Yes, of course (if e.g. some shards but not others broke/received an updated incorrect config). In fact, it applying to some but not other versions of the same app makes it look more likely to be a bug than intentional.