But first, there needs to be another city-state.
It's not right but it is what it is. I think it's better to accept this now rather than have to deal with our denial later.
Edit: I mentioned they could cut off all functionality. That was hyperbole obviously but they can cut off access to a hefty chunk of the API and replace what third parties are doing nonetheless.
Facebook? I'm unsure if Twitter's userbase is as married to the 140-char limit as Twitter thinks they are.
Maybe the elite who are willing to pay will migrate to app.net, but even if they do they're going to be set apart from people who don't want to pay $50, which means that even if I do sign up for app.net, I'm also going to have to keep my Twitter account.
See also: http://en.wikipedia.org/wiki/Creeping_normalcy and all the related concepts, eg boiling the frog etc.
http://www.fastcompany.com/26455/next-time-what-say-we-boil-...
IE needs more actual examples, instead of metaphors that turn out to be completely wrong in practice.