This would require years, maybe even decades of study. Apple can't just flip a switch and do this. Medical diagnostics is heavily regulated for a reason. It's entirely possible that Apple is working on this, or something like it. But you won't see it for a very very long time.

how can hospitals and doctors get access to this data? I've done some searching for a primary care physician that has the ability to integrate with Apple Health, and I haven't found any.

This exists. Until recently I lived in a city where this was possible, but my GP wasn't on the list. You can see a list in the Health app. But there are hundreds of thousands of practices just in the United States, many on incompatible systems. It will take a very long time for it to be available nationwide.