Have any of y'all ever heard of something called "Adobe Creative Cloud", it's...
It is literally trying to answer most of these questions for a set of titanic applications that predate the entire world wide web, it solves, offhand, at least five of these seven principles - it's (1) built around apps that have been working with local files since the eighties, (2) can sync your work between multiple devices, I just carry my laptop everywhere so I dunno how well it works, haven't played with the iPad apps yet so I dunno about those, (3) works just fine with no net access (though it'll cut you off if you don't hit the authorization servers every few weeks), (4) I am not sure how it solves the conflicting changes problem as I work solo, (5) your data's on your local device and in Adobe's cloud for as long as you subscribe, (6) okay well stuff's probably stored unencrypted, unless "I turned on whole disc encryption" counts (7) it's your own files and your own backup strategy.
That's five checkboxes out of seven, better than the 4/7 that "email shit around" and "github" get.
And it is relentlessly uncool. But it has been here for a good while and none of y'all have noticed it because it's built for artists.