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.