One problem podcasting has, and the Podcast Index is no different, is for it to be widely searchable, a directory is needed. That's what the Podcast Index is. They upload the database every Saturday for anyone that wants to use it instead of relying on the Index, but you'll always be 1-7 days behind the Index. The reality is though, most PC2.0 apps rely on getting feed info from the Index. One thing nostr may be good for is having several copies of the Index available so if one server goes down, the others are available as a back up. I don't know enough about nostr to say how that would work or if it would, but if any of you nostriches are up to the challenge, having the Index across several relays would be huge.