The news comes via Microsoft's own support site, which says the port (number 16 on the diagram above) will feature on "controllers released after June 2015." It also notes that only "compatible" 3.5mm audio devices can be connected to this port. Chances are you'll be able to hear audio through any headphones, but there will be some headset mics that won't work due to the pointlessly different way manufacturers order the conductors on their jacks. The PlayStation 4, and many phones, suffer from the same issue, so that's not really something Microsoft can control.