Here is OverDrive’s announcement about the switch to MP3 only:
http://blogs.overdrive.com/front-page-library-news/2014/01/22/overdrive-announces-plan-for-audiobooks-to-be-solely-available-in-mp3-format/
If the titles still expire, there has to be DRM involved. I believe these will still be .odm files that require OverDrive’s player or apps to translate to MP3s.
I have the small happiness that I can stop answering the “Why doesn’t this audiobook work on my device?” question, at least in terms of format compatibility. But not the bigger happiness of DRM really going away.
