While Carousel itself is considered to be a flop by some (http://techcrunch.com/2014/08/04/why-standalone-apps-are-sup...), I think the overall strategy seems correct, or at least, less wrong: go up the application stack based on their strong user base in the data storage layer.
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In the case of Dropbox, 4 months ago, I speculated about the motivations behind the Carousel product: http://kiyototamura.tumblr.com/post/82662241570/dropboxs-car...
While Carousel itself is considered to be a flop by some (http://techcrunch.com/2014/08/04/why-standalone-apps-are-sup...), I think the overall strategy seems correct, or at least, less wrong: go up the application stack based on their strong user base in the data storage layer.