Nobody is ever going to do that with this test, because the overwhelming majority of positive test results in a population-wide sample will be false, and the proposed diagnosis is devastating. This is a test for people who already have symptomatic dementia that helps confirm the diagnosis.

> Tell 50 million people they’re likely to have Alzheimer’s then tell them where to donate towards a cure, or treatments to slow it by a decade.

Pharmaceutical companies have spent something like $50 billion on developing Alzheimer's drugs with, well, the most furtive of straw-grasping to show for it. It's probably the most expensive single disease target (especially as things like cancer are families of diseases)... the failure to have good results isn't for lack of money, and merely throwing more money at it is unlikely to actually make progress towards meaningful treatments.