KDE share post-it note widgets + notes per activity

In the same vein as:
#228: Bookmarks per KDE activity and #229: kmail: folders per KDE activity

I want two seemingly contradictory things:
- share a post-it note widget among activities (which maybe implies the ability to share widgets unless we can specify a source file for the post-it content and configuration).
- have notes per activity.

The second one is already easily possible: have one widget per activity and each has their own notes. However, sometimes I want to access the notes in another activity and I'd like to be able to access them without changing activity (which might mean "waking up" an activity that was stopped).