The idea is to address two problems:
* For a focused task like character animation, there are a few favorite panels that an animator uses all the time. However these might be spread out over multiple editors or tabs. Which panels depends on the animator's workflow and the add-ons they use.
* When using many add-ons, the 3D viewport sidebar fills up quickly with many category tabs and panels.
Note there is no approved design for this yet. Some concrete features could be:
* Move sidebar panel to new or existing category tabs, overriding the default category provided by the add-on.
* Move sidebar panel to the toolbar side, so the toolbar becomes tabbed with one tab being the active tools.
* Pin favorite properties editors panel into the 3D viewport sidebar (would only be possible for certain types of panels).
* More intuitive control over which add-ons are enabled in which workspace, by e.g. right clicking on panel headers.
Drag & drop would help to make this type of customization intuitive.