Twitter has been just as "integrated" with Android for quite some time. And all Twitter Inc had to do was write an app, that used the standard Android API hooks.
In fact, my own Android phone doesn't even use the "official" Twitter app (which I find to be slow, heavy, and poorly done), it uses an even better and more advanced one called twicca. And the author of Twicca didn't need to "partner" with either Twitter Inc or Google Inc. He just wrote a better app, that again just used the public APIs.
It doesn't take a high-level corporate partnership, a 12 month product roadmap, and a heavyweight development cycle by employees of a set of large companies to add a deep and useful integrated feature to Android. It takes a single developer working in a cafe.
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