According to Wikipedia MHL allows proprietary connectors, and MHL-through-microUSB is most often done with 5 pins. Lightning is 8 pins + shield, so it would hav

According to Wikipedia MHL allows proprietary connectors, and MHL-through-microUSB is most often done with 5 pins. Lightning is 8 pins + shield, so it would have been possible for Apple to put HDMI signalling inside the devices, and get native 1080p/60 out. However, MHL-through-Lightning might have prevented the AV adaptor having a daisy chained lightning socket of it's own. Maybe that's why Apple jumped through these hoops.