There's been some press around the suggestion of Twitter formats, new bits of syntax like cont which indicate that a tweet is spanning two 140 character tweets. Like hashtags and @'s, this syntax is used to minimize the impact of the original 140 character limitation imposted by Twitter.
At some point, one has to wonder if hacks like this are indicative of a broader need: to remove the 140 character limit. Given recent research, only 3% of a sample of Tweets were submitted by text (see below). Most users are either using a web app, a desktop client or a mobile client.
Twitter has a culture of limiting the size of messages and I'd bet most users now, after a few years with Twitter, understand the preferred message length. Yammer doesn't have a limitation on 140 characters (which is refreshing).
Removing the 140 character limit, providing structured tags instead of hashtags and improving the experience overall may not be a step Twitter takes at any point in the near future because there may have been design decisions around the 140 character limit. But given the shifting usage modes, it might make sense.