> some kind of “brain fluid” dialysis

i think fixing the plumbing there may be a treatment for a bunch of issues given that for example the whole volume of the cerebrospinal fluid is normally refreshed 3-4 times a day (imagine changing oil in your car engine 3-4 times a day :) - i.e. any hiccup in the plumbing (even a temporarily one and even in the healthy people like a bad sleeping position) and you already may get headache, etc. One can imagine that any chronic performance degradation of the plumbing may lead to a bunch of issues (similar to say what happens in any other organ/limb when blood or lymphatic flow is degraded)

Specifically for Alzheimer's - we do know about direct importance of that plumbing system here - poor sleep is well correlated with Alzheimer's as during deep slow-wave sleep, the brain's glymphatic system actively washes away metabolic waste and toxic proteins, including Alzheimer-related plaques while chronic sleep deprivation increases the buildup of toxic brain proteins like amyloid-beta and tau.

That Alzheimer's surgery brings up another very important and pretty fascinating aspect - not only the Alzheier's may be not permanently damaging the brain, we may speculate that various things we observe as age related brain degradation may be not actual brain cells/core degradation and instead similarly fixable issues of just some utilitarian subsystems.