What I subscribe to--which is a lot--is a very limited window into what I would ideally like to listen to. first of all, the resulting feed is biased towards frequent posting, because I'll see those episodes more. it's also very much biased towards recency, which doesn't matter at all for many podcasts.
What I really want is a smart feed that's powered by collaborative filtering: what I've listened to to completion in the past is associated with what other people have listen to to completion, and I can just hit play next and start hearing a new episode, maybe from a podcast I didn't even know existed.
Ideally, there would eventually be sophisticated aspects of this like knowing when episodes are linked in a series and grouping them, so you wouldn't play episode five of Alexis Madrigal's "Containers" until you played episodes one through four, UNLESS episode five is being listened to way more than the others.
This could be monetized by allowing podcasts to pay to be inserted in the feed; maybe there would be a free boost given to new podcasts that appear to be being produced consistently.
Another thing I would love would be a social layer to podcast listening. If two of my friends listens to a particular episode, I want to see that, because not only does it mean I'm likely to like the episode, I know I can talk to them about it and even just feel like I'm experiencing the same thing they experience.