I was thinking the same thing not too long ago, then realised that there would be something lost in translation if it went ahead; whilst listening to episodes, the imagination takes control and helps build mental pictures about what is happening, what is going to happen etc. The voices, narration and sound effects are the reason why this is such an amazing audio drama, and I believe a book version would lose some of the magic associated with what makes it so good.

However, if they ever decide to make a movie or TV series, I'll upgrade my netflix subscription