One such very big problem is Alzheimer's. There currently is no cure, and there is no sign that a cure is likely anytime in the near future. However, recent advances in Machine Learning can be used to spot the tell-tale signs of Alzheimer precursors in PET scans up to 6 years prior to diagnosis with very high accuracy!:
The same techniques might be applicable to MRI (there are Machine Learning methods to infer information MRI wasn't designed for), and if so, will surely apply also to next-gen BCI scans. So, all of us might soon know, with very high accuracy, whether we will develop Alzheimer's in the next 6 years; and maybe that can even be pushed to 10 years, with a little loss in accuracy. What good is that?
Well, it is also believed that certain existing drugs can greatly slow the progression of the disease, or stop it altogether, if people start taking them long before symptoms appear -- the trouble is, though, that people don't regularly get PET-scanned:
"The experiments suggest that memantine might have potent disease-modifying properties if it could be administered to patients long before they have become symptomatic and diagnosed with Alzheimer's disease," Bloom said. "Perhaps this could prevent the disease or slow its progression long enough that the average age of symptom onset could be significantly later, if it happens at all."
"I don't want to raise false hopes," Bloom said, but "if this idea of using memantine as a prophylactic pans out, it will be because we now understand that calcium is one of the agents that gets the disease started, and we may be able to stop or slow the process if done very early."
So, with the very near-future arrival of good BCIs, Alzheimer's could very well be stopped in its tracks! -- If not by this method, then by some other method that only works if you catch it early. This wouldn't stop people who already have it from getting any worse; but it could have an effect like the improvements in sanitation over the last 150 years, that have drastically reduced the number of deaths and improved quality of life, by preventing infections from happening in the first place.
The same may also apply to ALS, Parkinson's, and many other diseases.