This is known as scalable coding and has been included as an extension or profile in at least every ISO and ITU standard since MPEG-2, see for example https://en.wikipedia.org/wiki/Scalable_Video_Coding (this article seems to be specific to H.264)
Thank you a lot for the proper technical term. Do you happen to know if it is widely used in web-based streaming applications (I would be surprised, as I don't think I encountered it before), if ffmpeg supports it (in the case of H.264),and if AV1 includes such an extension?