I think the hook is exclusive to the Beats earbuds so that they could differentiate between the AirPods and Beats. I don't think Apple will ever bring the hook design to the AirPods.Personally, I'd an appreciate a soft, in-ear "hook" to hold the units in place (like the older Bose QuietComfort).
I've never had an AirPod (any model) stay in my ear for more than a few seconds :/