Twitter - maybe there is no sustainable business model?

I hope this post will not violate CBS's honor code... :-)

In the exam, we have to come up with business models for Twitter. My question is what if Twitter owns only a platform while 3rd parties are taking advantage of the business opportunities associated with it?

At some point, the Twittwer guys will have to choose if they are following the open architecture which allows 3rd parties to use almost any data they have or closing some APIs to be able to take advantage of proprietary data and functionality. Both options seems bad and therefore the next question is how will Twitter survive.

• Does it has value as a unifying platform? For blogs, the space got very specific with different blogs competing to be relevant in very specific subjects. After all, if I am a financial investor I might be less interested in what users say about the new start-up in the valley. The word is loaded with information and people will choose to subscribe to a very specific Twitter. In Twitter's case however the process seems to be reversed. There is an underlying unifying platform on which 3rd parties are building very specific web sites. Will that trend continue? as an equity investor
  (for example)-- do I really need the entire network or am I better off with a service like www.stocktwits.com that will be independent?

• Can it provide users with value added experience that will make them stick around? The space between Twitter and Facebook can be filled slowly by adding more functionality to the current service and create a better user experience. However, any competition with Facebook seems highly unlikely - does the world need another social network?

Twitter and its founders will have a nice exit. They created an innovative service that serves as the atom of online communication. Many great, useful, services can be built on top of that.

Creating substantial revenues and sustainable business model will be extremely hard though.