I like these discussions because it gets me thinking about new ideas. I actually think saving a playlist as an RSS feed is the solution. RSS works for podcasting, and all the players know how to read the feeds. But, what if the players had another way of fetching the feed, like over a websocket. Right now, the feed is known by url. But what if it was also known by its event ID?
We could keep the underlying mechanism of RSS to send a file from a central server on the podcaster's chosen domain, but we can also broadcast the updated RSS feed to any RSS relay, and those relays can also store the feed. Put the eventID (or whatever the proper nostr term is to fetch a file and broadcast it) in the feed, so now when someone subscribes to the feed, they have the nostr id to find the feed from the RSS relays. It's backwards compatible with legacy podcasting, still uses a 20 year proven method, and updates the delivery mechanism so it's more reliable by having many points of fall back. Any podcast player can easily be updated to subscribe to a relay to fetch the latest updates to a feed, so it would also work with legacy players with very little update to their code.