I find the podcast culture incredibly frustrating. There's so much great discussion and information being shared, but in order to absorb it I either have to multi-task (aka ruin both tasks) or take a truly ridiculous amount of time per podcast compared with my reading speed.
I get that they're great for people with commutes or people who like running / walking and listening as a form of exercise, but I don't fit into either of those camps.
So just a podcast transcription service would be something I'd pay for!
Sharing a screencast of me browsing the French side of the internet. Many people don't pick up a new language because they think it's difficult, but in this case they'd be able to connect a written word (since it's a screen-cast) to a pronunciation. They'd also see how many words are shared and just pronounced differently, etc. (I'd be explaining what I'm reading).
They'd also see where I go when "I stumble on a word I don't understand", what I type into Google to get the information, etc.
Think lemonde.fr, latribune.fr, lesechos.fr. Mainly Politics/Economics, but one can also find "lighter" stuff for people to learn idioms and expressions.
Good luck.
A close analogy would be a radio show -- no one over teh course of a few decades has ever paid for a transcribed radio show
The podcasts I listen to have "show notes" and many of them are beginning to post a "table of contents" for each episode, eg "Discussion about $foo, 2:57."
Just my two cents