Standard Apple approach: unassuming name, nice core set of features, lots of UI polish. I’m sure most podcasting apps will experience some Sherlocking effect, but plenty of users won’t be interested for any number of reasons. I bet most are simply comfortable with their current app or won’t like Apple’s continuing affinity for needlessly skeuomorphic interfaces, and there are simply no killer features in Podcasts that you can’t find in even the basic competition.
Podcasts is a solid first-party replacement for the Music app’s terrible podcast implementation that is way, way overdue. Apple’s (perhaps intentional) tardiness to this market left the front door wide open long enough for others to stake their claim, and the fact that Podcasts isn’t built into the OS will give third-parties a fighting chance. The majority of Podcasts users (especially those who stay) will probably be people who are new to iOS entirely.
I wouldn’t be surprised if third-party iOS podcast apps experience the Instapaper Effect, where Apple’s entry in a market causes it to contract a little at first, but then turns the majority of interested customers on to the world of what else is available.