A problem, however, is that subscriptions are desirable revenue streams regardless of continuous operating costs. A product I can buy for a largely concrete exchange in value, whereas subscriptions will (at best) go to value in the future that I may not have chosen to buy.

I notice that you feel bad for the devs of the podcast app, but not so bad as to give them the word of mouth marketing they no doubt hopped would be the fair trade value of early lifetime memberships.