The fact that I can easily play almost any audio or video file in my iOS is just another reason I've stayed with Dropbox over the past 10 years.
The new feature I'd love to see the ability to do a 2x or 4x speed on the audio/video inside the iOS app.
This is available on the web interface.
Please oh please put it in the iOS app as well.
Life-changing for audiobooks, webinars, trainings, etc.