Overcast just did this. If you remember Tweetie (ancient Twitter app on iOS) they built a little bespoke network as well.

It's certainly possible, but not scalable. If your goal is to support your own work and you have the hustle and editorial eye, you can make money.

Keep in mind that the big players can wipe you out in a second. Overcast exists because Apple's benign neglect of podcasts. They can wake up at anytime and wipe the app and ad market out.