Currently Favourites is a setting that is mainly set by the individual Applications Menu type Plasmoids, however this could potentially get messy with different Plasmoids potentially adding different favourites.
To resolve the potential for this issue, and make it easier for distributors to change the default favourites in Applications Menus, I propose that it be moved into a global setting in say kdeglobals that all menus don't automatically, on creation, set the value of but can still manage what is added and removed from favourites as the user adds or removes favourites as usual.
In other words, make the setting a global setting and make menus NOT edit that setting automatically unless it's because the user added more or removed favourites through them manually.