"It's a controversial and complicated idea. "

It is neither controversial nor complicated to detect some cancers by scent.

Taking the "headspace" of something is also not really complicated.

There are people who can reliably smell/detect Parkinson:

https://www.npr.org/sections/health-shots/2020/03/23/8202745...

You gloom on one aspect, the smell. OP focuses instead on full body scans themselves, and the irrelevant issues with everyone's bodies they would highlight.