I didn’t expect a phone upgrade to affect my running. (Such 20th century naiveté.)
The trouble had nothing to do with the iOS 8 HealthKit API. This is very basic. My phone didn’t fit in any of my gear. My handheld bottle with phone pouch was too small for my iPhone 6, so was the storage pouch on my hydration belt.
I found some armbands for the phone, but I never liked those. Plus, I don’t need another weird tan as a result of my long runs. I found only one pair of shorts (which don’t really fit) with a pocket that I can put the phone in.
I can leave the phone on some runs, but I don’t feel comfortable without it for the most part. Good luck to those 6 Plus owners.