In fact, with nearly 320 million users, media companies already believe they need to be on Twitter to reach their audiences. With a billion users, it would only be more true.
Twitter's only incentive is its use as a broadcast platform for people who are, in general, otherwise famous. People hop on to interact with and read content from them. If large numbers of this group decided that Twitter represented competition and not an asset, they'd dump it and the attraction would go away.
For years the only place I heard of Twitter was television channels desperately begging people to get online and tweet them. It has finally penetrated to the point where most fairly tech-savvy people have started an account and issued 3-4 tweets, but that took years of constant pushing by mainstream outlets.
If Twitter accepts the role as a news outlet, they're still in an awkward position. Conventional news networks are already grasping to maintain relevance in a world increasingly self-connected. If Twitter overtly embraced that as its primary value proposition, all of its support from media companies, which are really what propped it up IMO, would vanish overnight.