It would be nice to have the possibility to give sort of a HTML "master" with all the animations, buttons, interativities, etc. as can be seen in the uploaded document. That way, this master could be storaged where the client wants: own server, own PC, historical arquive in their web or wherever they would like.
Also, it makes it easier in case the designer/agency using Publish Online breaks parts with the client, breaks parts with Adobe, ends activity for good or any similar situation. And I'm pretty sure it would also be cool for Adobe to not have all that occupying space in their servers forever (even if they eventually start charging for that, in which case being able to download the content as it's seen would be needed as paying any plus should be an option and not an obligation)
I know some plugins offer this option (WebPublication for instance) but I think this must be included as an InDesign Publish Online own feature as these plugins charge unfair amounts, taking advantage of the fact that the option is not offered.