Some of the hosting services already offer this in a kind of sort of way, and spotify seems to be trying to become a youtube of podcasts. I wonder, if all podcasters uploaded tagged episodes to YouTube, would its algorithms automatically recommend others? Of course that detracts from download stats etc, but maybe the people who really want to grow their audience wouldn't mind.

A paid hosting service would find it difficult, I suspect, to gain traction, although you could probably build something neat on top of AWS.