Podcast Type
When editing a podcast, you can now specify whether the show is Episodic or Serial. Episodic is your best bet for shows that publish on a regular schedule. Select Serial if your podcast is released by seasons, or if you want listeners to start with the very first episode.
Episode Title and Clean Title
In addition to the normal Episode Title field you now also have "Clean Title" available as an optional field. Here's an example of how Episode Title and Clean Title would work in practice:
Episode Title: S2 E3 - Example Title
Clean Title: Example Title
The idea behind the Clean Title is that you only include the episode's title and not any other explanatory information like season or episode number.
Episode Type, Season Number, and Episode Number
Each time you publish, you may now specify whether it's a Full Episode, Bonus Episode, or a Trailer, and the Podcasts app in iOS 11 will surface each episode type differently.
If you're editing an episode for a Serial podcast, you may now optionally organize your episodes by Season by specifying an integer.
You can identify an episode number. This is designed to be used in conjunction with season number. For example, you will now be able to have two different Episode 1s. You can have Season 1, Episode 1 and Season 2, Episode 1.
Other Apps
Overcast
Overcast announced via Twitter that they will support the new Apple Podcast tags for Season and Episode Number. Specifically he said this will change the display of episode lists but not have any behavioral changes.
More Resources
Want to learn more?
You can watch the Apple WWDC session on Safari or the WWDC app. Here's a link:
The slides presented at the session are available here.
The RSS spec updates are summarized here.