I dunno, I used a lot of RSS feeds and feed readers back in the day. It was a good digest mechanism before Google News and social news. Now it just seems a historical oddity.

Sure, maybe podcasts use it as an underlying protocol, but users' experiences depend more on the front-end client (some app) than the playlist protocol. It's not really a discovery protocol either; turns out having a central index like Spotify or the podcast apps do works better anyway.

I think it's irrelevant in the sense that it could be trivially replaced by app-specific implementations, and few people would even notice anymore.