is the headphone jack on this mba a TRRS one, i.e. does it also work with iphone-like microphone + headphone set? can you point to some official source?
I think it is. You can check for yourself by opening System Information on your MacBook (alt-click the Apple logo in the menu bar and choose System Information), click on Audio (in the Hardware section on the left) and click Intel High Definition Audio. If the Headphone section mentions Combined audio-output (or even easier, if it mentions iPhone Headset) then you will be able to use a headset.
*My own Mac's language is not set to English, so the exact translations might be slightly different, but you'll get the point.