updated 03:51 pm EDT, Thu August 28, 2014
Should address one central fear
Though developers might potentially sell the data anyway, anyone caught doing so would have their apps kicked out of the App Store. Advertisers could theoretically use the information to market products like supplements, accessories and medical treatments.
Apple itself will also have to be careful with HealthKit data, since it's treading into areas regulated by government agencies like the US Food and Drug Administration. The company is believed to have met with FDA officials last December, presumably to discuss compliance with federal guidelines and laws.