A specifically Nintendo branded one I mean. Given the accessories they already have lined up, I wouldn't be shocked to see it.
If it will happen, I can see something Hori related.
There are? Any link (Amazon, etc.) Might need to look into it, in case headset cable isn't long enough (it should be, but better safe than sorry).
There are these kinds, but this one is a bit bulky and requires to plugged to an AC power outlet. Probably because it can drive loudspeakers
http://www.logitech.com/en-sg/product/bluetooth-audio-adapter
There are smaller ones like this too:
https://www.amazon.co.uk/dp/B005NDDEVQ/