Scenario: I have a sync folder that I share with a friend. We both upload files there so we can both see and talk about them.
Problem: One might not need a file anymore and delete it, even though the other still wants to keep it.
Solution: It would be great to have a new folder type (or special access rights) called "Collection". This folder would work as follows: Files uploaded there are visible to every identity the folder is shared with. Each identity can delete any file, but a file is only deleted once every identity has deleted it. This is similar to Selective Sync, but just doesn't have the option of "Delete on all hosts".
