Serial works this way because it uses a lot of interviews from external folks. That would not work at all in writing. You have to design for reading or design for podcasting, there's rarely a case where something works well on both media.
Yes, but I think it's probably possible that interviews could be conducted. Maybe interviews were even already conducted and recorded for this approximately 50,000 word series...
No but really turning a long text into podcast can really add to a work. Just Look at something like Serial.