chirp-260 (1) Metadata has long been part of Twitter applications. Viewing conversation threads or learning about a user’s location has changed how users interact with content and have provided third party app developers with great opportunities to innovate on Twitter’s platform.

Ryan Sarver, Twitter’s director of platform, announced today at Chirp, the Twitter developer conference, that annotations can now be added to tweets. In other words, any kind of metadata can be added to any tweet; it’s up to developers to decide what kinds of apps they build to showcase what kinds of metadata.

Sarver said he wants to see what kinds of emergent behavior and apps appear rather than trying to predict or force user behaviors by narrowing the spectrum of metadata available with tweets. Leaving that decision up to developers and users was the best path, he told the audience at today’s show.

However, some developers are wary of working on more Twitter-related projects as Twitter expands their features and acquires some applications. There is uncertainty in this ecosystem as to whether developing for Twitter is still a viable startup plan. One developer, who had been in acquisition talks but noted that Twitter’s interest had cooled, said anonymously, “I wish they would tell us what they plan to develop and what they plan to acquire so we can get out of the way.” No one wants to build an application — let alone get funding for a new business — that will become suddenly obsolete once Twitter makes an official feature from a third party application.

What do you think: Will the Twitter ecosystem continue to grow as a vibrant part of the startup community? Or will it become a network of unfunded, unsupported side projects? What kinds of metadata would you like to see attached to tweets, and what kinds of applications or functionality could that data be used to create?

Developers can check out for more information on metadata for tweets and other projects, such as the all-new User Stream API, starting later today.