I have two feature requests for the animation ghosting.
First, it would be nice if the ghost lines were heavier. They are hard to see at higher screen resolutions. Perhaps there could be a setting for the line weight. Having the keyframes highlighted would also be helpful. (It may already do this, but it's not apparent.)
Second, it would be nice if the ghost lines had their own color setting. Currently, the ghost lines share the wire frame color. But this makes them hard to see against the armature since the armature also uses the wire frame color setting.