As somebody who doesn't need to be able to attach images, videos etc and therefore has no use for the 10Gb of storage (outlines wouldn't be using that space at all), I think I'll give it a miss.
Being able to store the URL of outlines from the same site isn't really worth an extra $15 a year to me, I'll just put it in the notes.
Really not sure why linking to an outline is being treated the same as uploading a pic or video, storing it and linking to that, if anything I can see it harming take-up of outlines. But that's your choice, I guess.
Import from OPML format would be extremely convenient for me - then I can import my CarbonFin and BrainForest outlines. Would love to have them all in one tool.
Plus, as per several mentions,Outlines for iOS would clinch it. Already a Pro Plus user, but this would add to the overall happiness factor ;).
Would it be possible to add Box.com to your upload menu options. In addition, what would be fabulous is to add the same menu to the URL as both Dropbox and Box give addresses at the file level this would allow dynamic updating.