The idea of sort of "mini-series" podcasts like that might appeal to both listeners and DIF. Do however many episodes until you've exhausted the subject, then stop. In a way, they'll be more "timeless" than the current movie episodes, the kind of thing that will pop up in searches and bring new people to DIF as time passes.
As for possible subjects, I would love talk on the tradeoff between historical accuracy, and... well, being good Use A Bridge Too Far as an example, as I need to know what the hell isn't working...