One place this would be useful is a DVR. You want to record the last n hours of video and discard anything older. And it's not inefficient. It just requires a lot of careful engineering that's probably not worth the bother.
It's unnecessary to create a filesystem-level support I think, since you could make a circular buffer holding a video stream in a file with some constant size that is approximately n hours of video. With some clever tricks you could even keep the format compatible with existing video container formats.
Or just use a set of files, each holding N minutes with, perhaps, some overlap + an index file. No real need to over-engineer things here.