Ability to create multi-configurable windows without having to use the curtain walling approach, thus retaining the Window category.
This could be achieved using the same curtain walling logic i.e. grid setting out.
Didn't bother searching first did you?
https://forums.autodesk.com/t5/revit-ideas/assign-a-curtain-wall-as-a-window-curtain-wall-family-cre...