People already use Twitter for long messages all the time, but due to the character limit they have to do it by posting images of text or other ugly workarounds. If Twitter wants to give priority to short messages, that's fine, but forcing people into workarounds is just stupid. They had the same thing already with photos, people used TwitPic and other workarounds for a long while until Twitter finally started to allow images. It hasn't killed Twitter, quite the opposite, it made it more versatile and useful. I would expect much the same happening with long text support. Not supporting more than 140 characters isn't a feature, it's a leftover from it's SMS beginnings.