Marco could theoretically bootstrap a directory based on user subscriptions (the RSS feeds are polled server-side, not on every client), but then you still have the problem of how new podcasts get added.
The iTunes API is poorly documented but completely public. No reason not to use it.
IIRC Marco also said that he is happy with the status quo. He really doesn't want to have responsibility for any moderation/curation and is happy to defer to Apple in that matter. This was shortly after Apple removed Alex Jones' podcast from the directory.
The iTunes API is poorly documented but completely public. No reason not to use it.
https://performance-partners.apple.com/search-api