People use Dropbox on their iOS devices because they want to share information between Apps. And they use Dropbox on their Macs and PCs because they want to share information between people and computers. Why not make iCloud better at both, and lift the superimposed limitations on sharing information between apps that gives Dropbox a linchpin in iOS?
It’s a really good sounding idea, but I think it would break the simplicity of iCloud if done improperly. There is one way I think that could add such a feature without over complicating things: allow iCloud apps to all have “Send to…” buttons in them.
If I am working in Numbers and have another app, on either my Mac or iOS, that has registered to be able to open the file type I am working on a user can open a share sheet that shows apps and sends a copy of the file to that app’s iCloud bucket. This would be simple, non-destructive, and easy to explain to all users.
Of course this opens the can of worms that is the “Open with…” dialog currently on Macs, where all too often the sheer amount of apps listed is overwhelming. That is one aspect I don’t know how to overcome, because a preference to limit shown apps would defeat the entire purpose of ‘ease of use’.