It is not really mainstream, but podcasts become more widespread, especially since established media (tv channels and radio stations) distribute their content as podcasts. Self-made Podcasts loose importance? I do not know the numbers. It might be the case and there is Youtube too, similar to Podcasts.
In education it seems to be the same: Lecture recordings prevail by far over student authored podcasts or learner generated content. Perhaps the model does not fit in existing education. And students would perhaps prefer more lecture recordings than seeing effort spent in podcast production from scratch. Perhaps both models cannot even be compared.
Podcast production could be seen as a media literacy skill, producing audio or video to transport a message. Rhetoric skills can be trained. All side effects to teaching. But does it have a similar necessity in the process of teaching as for instance texts? Why use it when I do not need it?