But another expected scenario is an attacker with a nondescript car and a wifi router inside who can sweep the neighborhood searching thru walls for Person X.

Hmmf, nasty, but labor intensive. Is it working on backscatter ? because your devices shouldn't be responding much (beyond ping / authentication query level).

Also, at that point they can just use whatever fits in a van, radar, IR scanners, who knows what, fucking X-rays maybe, don't know that they'd bother with this.

Avoiding it being deployed at scale to everybody's router might be more important.