iPhone and MacBook Pro with a single wireless headset
I know there are some Bluetooth headphones (such as these ones that I can talk about from personal experience) that come with an optional audio cable, enabling them to be used as a standard pair of wired headphones in case the pairing malfunctions or something. It has the really awesome side effect of enabling the headphones to play two streams of audio at once: Pair them with one device wirelessly and plug them into another.

I know, it's not a perfect solution, but it's the best one I've seen so far.