You're spot on. Research would be more difficult.
And you're spot on there, too.
Let alone the general-citizen perspective that this is all just amorphous data, and generally our privacy should be protected, and generally mind-fluff background confetti, this has one very real consequence I can think of.
The welfare state doesn't fare well; private health insurance is more meaningful. I have it, particularly as a shield for my kids, and it's bloody costly. But there you have it.
The only way to prevent health insurance rates going up is for there to be decent competition between providers. Now if I want to switch providers, like with my car, I can either go 'don't declare history' or 'do declare history'. Depends on the circumstance.
But if I want to keep my history quiet, well, there will be an open market on this data to determine exactly what's up with me, if anything. We will see data brokers sitting between the medical community and these companies, making sure they get exactly what they want.
You then get a twist between actuarial predictions of your health, and the average. Currently, most insurance works on such big averages that it's a fairly communal thing. I'm healthier than most people, so subsidise sicker people. Fine.
But when the actuaries can pinpoint a likely health profile, the insurance argument falls over. It simply becomes a matter of charging people what you know they'll cost, plus profit - the sicker portion of society will not be able to afford it.
They return to the inefficient, politically swung NHS. To balance the books, it makes financial sense to diminish treatment for the elderly. This will happen, and is happening. They find it harder to have a voice.
So the whole idea of a health system will eventually return to the 18th century method, whereby you get what you can pay for.
And the societal benefits of a positive and efficient health system will evaporate.