Jack has discussed this. It won't happen. Even in 5 minutes a tweet can reach MANY people, and then it would be able to be changed entirely?

Twitter won't get an edit feature, it just doesn't work for the platform. The only way I see it happening is as an 'undo' send feature like Gmail has. You can see the tweet for 15 seconds before it actually goes out. This has also been discussed as an issue since Twitter is supposed to be real-time, but maybe certain people wouldn't care and enable the feature