Season 2 is premiering this month, according to an interview with Sarah by Glamour magazine. Both seasons will be "exclusively" streamed on Pandora, but this doesn't mean much because podcasts don't usually stream anywhere.
Koenig still hasn't revealed the subject matter of season 2, other than noting that it's "controversial", but it's highly likely to be the case of Bowe Bergdahl. There is also going to be less downtime between seasons 2 and 3, which is being worked on right now and set to air next spring.
I still think Adnan didn't do it but was an accomplice.
Source: Engadget, Glamour