There are a number of open source podcast players; some are web-based, some are (like AntennaPod) native apps. The Pocket Casts player is open source, but the server it links to is not. Also see Podfriend and Podverse (I think).
But I don't see anything broken with RSS feeds that specifically Nostr can fix. Incessant polling is fixed with either websub or a blockchain solution like podping - unsure of what else needs fixing.