If you listen to hearstartup.com you'll find Marco investing in Gimlet Media which is all about creating a lot more podcasts like Serial so he's very much in favor of the format.
I only recently started listening to Startup, and haven't caught up with it. It's interesting to see Marco moving from the "creating a podcast" game to the "investing in podcasting" one.
Pretty sure that Marco is investing in Blumberg himself though. He says that in the episode interviews.