I was envisioning (as long as we're fantasizing) more of a tagged imaging technique, vs. (or in addition to) an assay. It's not just the presence of the TAU bodies, it's their architecture as clumped masses in relevant CNS tissue. Maybe more like the mentioned flourene-tagging amyloids under PET scan. Plus it avoids the LP.

Both assays and scans are necessary. Assay for basic detection, with a blood test being minimally invasive and supporting immediate post-trauma testing. Scan for functional diagnosis, e.g. what areas of the brain/spinal cord are affected.

There exists still the problem of differentiation from Alzeimers. Hopefully there is some kind of structural or histological differences, after all they are different disorders, despite the amount of overlap.