I'm requesting a headphone icon for when headphones are the audio output, instead of reusing the speaker icon. 1- It would help users to know when the headphone jack is connected properly, or if it is connected at all. 2- It will become even more necessary once the feature from Bug 440536 gets implemented and both speakers and headphones are active (Perhaps with a diagonal cut showing each side of these icons).
We have one already; it's called "headphones" There are even colorful versions under "audio-headphones".