Twitteratis have been asking for an edit button for the longest time. But that may still be some time away as the company does not want to "rush it" and will take a considered view of a use case for allowing individuals to make changes to their tweets.
"We have been considering edit for quite some time but we have to do the right way. We can't just rush it out. We have to make sure that we are actually solving the predominant reason why people would do it first and foremost and not making something that is distracting or