While I would love to have the job of Futurist (mostly for the cool title), I just not that good at predictions. However, I’m willing to go out on a limb and forecast that this idea will probably not work. Radio stations are now trying to charge a subscription fee for downloading podcasts of their content.
This particular model of squeezing a dime from the net will flop for the same reason that commercial radio listenership is falling. Most of the broadcast stuff is crap and is crammed full of ads. Anyone willing to pay to listen is probably going to buy one of the satellite providers to get more specialized programming and avoid the advertising.
The big exception right now is public radio, content many of us already pay for. Between their great programs, most of which is streamed on the web (and thus can be captured), and other small bits of good broadcast material that can be recorded with Radio Shark, I have more than enough good stuff to make the commute tolerable. Why would I pay for the files?