This is potentially very bad for podcasting as an open, RSS-driven medium. Welcome to a world of "Spotify exclusive shows" not available on your favourite podcast player.
What if Spotify is my favorite podcast player? Since I pay the subscription it's much better than other one's with ads. I got as a music player first, getting all of my podcasts there as well is a nice benefit.
I don't really see how this hurts podcasting though, pretty sure you can still host podcasts elsewhere, just that with Spotify you could reach a greater audience.