I am sure there are but perhaps you could highlight the most common/not superniche ones that aren't better served by the rear-facing camera?
A few other usages of the front-facing camera include but are not limited to:
1) Capturing images of camera-averse people or pets.
2) Capturing images of locations where the front-facing camera cannot be seen. Like the outside of a building photo'd from the roof, or an appliance nameplate with limited access, or the ports on the back of a display, etc.
3) Surreptitious photos. E.g. capturing illegal activity by others without getting into a confrontation.
4) Someone already mentioned examining facial hair or whatever.
5) Shooting from potentially unsafe locations (rock faces, ladders, etc.) sometimes the rear camera can be much more convenient/safer.
6) Achieving truly spontaneous image captures. Almost all people and animals subconsciously adjust their look when they know that a camera is aimed at them.
7) Capturing a pic from high angle of view. E.g. holding the camera high and shooting down.
8) Capturing a pic from a low angle of view. E.g. holding the camera at ground level and shooting up.
I do not know what you consider
superniche, but I take one or more of 1 through 8 above pretty much every day. So I do appreciate improvements to the front-facing camera even if the rear cameras are more important. Note that taking
selfies is not in the list.