If the above feature is implemented, and if we could have a feature to retrieve the material names (not names of Material Assets!) for each "side" or "face" with a script, it'll be easier to implement scripts for controling textures and other "face" related features for several objects at once, without having to first create mappings between face / side number and intended material face.
See the provided images for two objects that are intended to share some materials, while they differ in other ones. I envision having those material names, listed to the right in the pictures, retrievable by for example llGetObjectDetails(OBJECT_SIDE_NAMES), which could return a list like so:
["Floor", "OuterWalls", "Roof", "Underside", "WallEdges", "WindowPanes"]
Which means that "side 0 is named Floor", corresponding to the index.
An object not having this information should return an empty string for each unnamed side.
This makes it possible for a script to automatically map side numbers with intended materials for them. A viewer such as Firestorm with a scripted "bridge" could also potentially retrieve the information to show in the UI.