Vine is about forcing creativity and curation of the visual world around us. 6 seconds really limits the amount of content you include in order to tell a simple story. The 140 character limit on Twitter, whether purposeful or not initially, also forces this creativity and simplifying a message to give as much meaning possible in as little space possible.

Imagine if Twitter had / was able to acquire Instagram. That, plus Vine, and I'd say Twitter would be on their way to helping rapidly kill Facebook; Now Facebook's death with just be a bit slower, and they may own some more assets that might be worth something.