And I wonder if anyone has ever tried to write a play or read a story with multiple voices? Kinda like radio theatre?
Not quite what you're referring to, but last year I was part of a group that did a podfic of In From the Cold (a J2 AU fic, which can totally read as original fic if you aren't familiar with the characters) where we switched off POVs, I had Jared's part. So, if there was a conversation happening from his point of view, I would read everything, even things said by other characters but if it was Jensen thinking someone else would read those parts.

If you're interested in group readings, the archive has a colaberation category. I'm not familiar with them but QueensGuard was mostly read by a single reader, but there were little news clips at the beginning of each chapter that were read by others. The ones by Fangirl Productions are taped public readings (mostly one reader, but you can hear the audience reacting, often giggling). Written by the Victors was probably the first large scale group production in podifc. If I remember correctly (it's been years since I've listened to it) there's a reader reading the story of what's going on in Atlantis, but much of the story is told through articles being written about the people of Atlantis from Earth's POV. And each scholar writing about them is a distinct reader.

Podfic is still just becoming popular so people are still experimenting with things. Also a lot of podficers podfic in isolation so it's hard to do radio type plays when the characters in question are all over the world. :)