As we look toward the next decade, the distinction between "side entertainment content" and "popular media" is dissolving.
Within five years, major studios will release two versions of every major property simultaneously: (the traditional movie/show) and The Deep Dive Cut (a version of the film intercut with director commentary, trivia pop-ups, and behind-the-scenes footage). The side content will not be an extra; it will be a track on the disc.
For creators, the lesson is clear: Do not treat your extras as junk. Treat them as the second act. For consumers, the warning is equally clear: Don't get so lost in the commentary that you forget to feel the original emotion.
Likewise, the largest podcasts will not be original concepts, but "companion casts" attached to massive IP. The term "side content" will feel quaint, because the architecture of popular media will have permanently bifurcated.