There’s a huge number of leads in the search for markers. It’s just that nobody is talking about it. I’ve never met a lay person who had any clue of what’s going on in the space
They implanted a chip in the patient's (yes, n=1) brain, which they trained to detect when the patient is going into depressing thoughts. Using Deep Brain Stimulation they terminate the signal propagation of that neural pathway.
Similar techniques have been used to treat Parkinson's.
I’m talking about a simple, non intrusive way of testing someone’s mental health without talking to them. That stills seems far off on the horizon. Maybe some MRI research might be able to take us into the future in that regard.