We want every person around the world to easily express themselves on Twitter, so we're doing something new: we're going to try out a longer limit, 280 characters, in languages impacted by cramming (which is all except Japanese, Chinese, and Korean).
Twitter's largest issue* is gaining and retaining active users. The platform hasn't meaningfully grown in many consecutive quarters. While I think it is totally fine to expand the character limit on tweets I do not believe a single holdout will come to Twitter now because of this change.
As far as my opinion about going from 140 to 280 I'm with Fred Wilson:
I don’t like the constraint when I compose tweets, but I love it when I consume them.
I'm sure the current user base will be split on this but I sit here thinking if I were on the Board of Twitter I'd be asking "is this all there is?"
* This is their largest issue purely because they are a public company with revenue based solely on ads.