The reality of healthcare interoperabilty is going mainstream: Apple Launches HealthKit To Share Vital Stats With Nike, Mayo Clinic:
The problem Apple will run into: No one agrees on how to measure even very simple health metrics, ...
TL;DR: iOS 7.1 to iOS 8.0 API Differences (search for 'HealthKit' on the page).
UPDATE (8/18/14); Apple - iOS 8 - Health