I once started writing a podcast app like that. As a listener I would reallly like the idea. Unfortunately I don't see why a podcaster would do the job of adding metadata on my platform if they don't get anything out of it. If it was a core of their value proposition, they would probably use a mooc platform and not a podcast.

Then I though I would probably need to build a more useful tool to manage other needs of a publisher, like website, feed generation, pushing to multiple platforms, etc. That way I would have all sorts of metadata for free AND I would provide value to the publishers (automatic publishing to all other platforms). I could host the content too and give them download numbers, could post listening habits from my app, and all that. But that is a lot of work though, before I can provide any value to either the listeners or the publishers.

Then I listened to a podcast about the podcast ecosystem (how meta) about how podcasters actually benefit from the ecosystem being so distributed. If there was a single format for metadata dictated by a single company (would probably be apple) it would eat into their advertising revenue. They would not admit it, but it's actually good for publishers if they only have rough download numbers. Without clicks, they can just make up their numbers, and sell ads even though everyone fast forwards on the ads. If they had actual clicks, their revenue would become dependent on it.

For sponsored podcasts you're right. But much of what I listen to doesn't have advertising, or it's indirect in the form of interviewing guests who promote their products.

For example, one of the podcasts I really like is run by a guy who a) knows a lot about real estate and b) sells a SaaS product for people who want to do what he does. He frequently references show notes, PDFs, webinar signups and the like in his show, and I engage with most of that stuff... if I remember to do it when I get home.

In his case the value per customer is quite high, so he would probably make the investment in rich media. He doesn't have sponsors and so isn't beholden to click through rates.

And I'd wager that's true for the vast majority of podcasts. A handful make money from advertising because they have really large audiences. The rest do it as a hobby or to promote their businesses.