The 1.5mm jack, on the other hand, is the standard audio connector for just about every consumer-grade device in the world. Not sure what the upside is for Apple, even with them owning Beats.
So, let's suppose they go this route: I think that an adapter could be ridiculously small. It needs to wrap that audio connector, hold it tighter than a lighting connector holds a lightning cable (should be fairly easy), add about half a centimeter for the lightning plug, and have room for some chip doing lightning-to-audio conversion.
A lot of speculation? Yes, but if it works, I can see them go that way. The main problem is the case of people who use a single headset with iPhones and non-Apple devices (extra weird idea: when do we see lightning in iMacs?)