A simple addon to the Eq DSP page that allows you to apply a bit crusher effect to playback.
Not many media players on Android have this feature, so it can be a selling point. Plus it sounds unique and cool!
Other application solutions:
There are classic desktop examples of media players with this feature built in or provided by a plugin, such as foobar2000, Audacious, and Winamp.
Unfortunately not really possible for the moment unless you know how to write it as an audioprocessor in ExoPlayer.