Amazon could make these available through a simple RSS feed or export feature, but they don't. The only way I can get my hands on them is to scrape their website, which depends on some fragile scripting and is subject to their terms of service.
I really like this idea, but without some kind of positive government regulation, I don't see it happening. At least not in the sort of meaningful ways the OP envisions.
A simple example off the top of my head. Let's say there's a popular app that collects your pulse from your cellphone somehow, and that data is stored in your "Personal API" in some format. Some scientists write a routine that scans people's pulse patterns (with their permission, say) and warns them of possible risk factors. Later on hospitals start feeding their pulse data into the same personal API, but in a different format and using different units (bpm instead of bph, say), because they've never heard of the cellphone app.
I take "discoverability" as a general concept addressing how the scientists' routine might discover that the hospital data exists in a person's "Personal API", discover that the thing being measured by the hospital is the same as the thing being measured by the app, and discover how to map both formats into a common workable format and units.
There was that interesting article a while back about how Target was able to figure out a teenage girl was pregnant before her own father did:
http://www.nytimes.com/2012/02/19/magazine/shopping-habits.h...
It glosses this point:
Target can buy data about your ethnicity, job history, the magazines you read, if you’ve ever declared bankruptcy or got divorced, the year you bought (or lost) your house, where you went to college, what kinds of topics you talk about online, whether you prefer certain brands of coffee, paper towels, cereal or applesauce, your political leanings, reading habits, charitable giving and the number of cars you own. (In a statement, Target declined to identify what demographic information it collects or purchases.)
I'd be very curious, and a little scared, to see all this kind of information collected on me.