We've written , at length , on Twitter's attempts to safeguard the profitability of its network against all-comers , so this shouldn't come as any surprise: the company has confirmed that, from March 2013, they will begin enforcing a de facto ban on third-party apps.
The ban is revealed in two passages in a post to developers  by Twitter's director of consumer content, Michael Sippey . The first tells developers that the company's "display guidelines " will become "display requirements", while the second explains that from now on, any service with more than one million users will need special permission from Twitter to continue growing.
The display requirements are an incredibly strict set of requirements which not only hit their intended target, third-party consumer clients like Tweetbot, Econfon or Ubersocial, but also a huge number of unintended ones – Jason Kottke  says  that his aggregation site Stellar  meets just four of the 16 requirements, while Marco Arment, developer of the popular Instapaper reading app, thinks that his "liked by friends" feature will have to be pulled, or at least rewritten, to comply .
Other rules look likely to hit services like Flipboard (which breaks 5.a., "tweets that are grouped together into a timeline should not be rendered with non-Twitter content. e.g. comments, updates from other networks") and Storify and Favstar (which break 3.b., "no other social or 3rd party actions may be attached to a Tweet"). Or they would, had Twitter not clarified that actually, those latter two are the "good" apps. Ryan Sarver, the company's director of platform, tweeted that  they are what they want in the ecosystem.
This ought to be good news - two of the most useful third party apps are safe - but in fact, it's even more upsetting. It shows that, from the off, Twitter's rules all contain an implicit "...but you can ignore these if we like you." If that is the case, it's not hard to imagine that they also contain an implicit "...and no matter how well you follow these, if we don't like you, you're off the service." Everything using the network does so at the capricious whim of its overlords.
The million user limit is even more indiscriminately applied. Any application, no matter what it does or how well it complies with the published rules, needs to "work with [Twitter] directly" to get more users than that. It is, essentially, a rule that gives the company carte blanch to pick and choose whether any company getting too big can be allowed to grow.
Most companies try to keep customers by keeping customers happy. Twitter is clear in its intentions: it wants to keep customers by making it extraordinarily difficult for them to leave. It is holding its network hostage; you can go, but you can't take your friends with you.
In July, when Twitter first acted on their intentions to block clients which "mimic or reproduce the mainstream Twitter consumer client experience" I wrote that:
That is bad enough for the company, but up to now, the users of those apps are a minority on the service. The vast majority of twitterers use the website itself, or one of the official clients on mobile devices.
But with these changes, Twitter hasn't just hit the apps used by a small (nerdy) minority of users. There are going to be very few Twitter users who aren't affected in some way or another by this attempt to turn the site into a Facebook-style walled garden.
We like to make analogies to Apple in tech blogging circles, so here goes: this is the moment in Twitter’s life where they kicked Steve Jobs out of the company and told Sculley to run it.