It's no different than browser fingerprinting. "You can just use a VPN/spoof your user agent!" It's not that simple. Just like how browser fingerprinting has evolved to the point where it's virtually impossible to get around, these real world systems will follow suit. Hair color, eye color, skin color, the types of clothes your wear, your gait, height, gender, path you take through the store, car you drive, license plate, stores you frequent, heck... even where you choose to park or which door you choose to enter could all be used identify individuals/families.
Keep in mind, just like with web analytics, these solutions will be provided by 3rd parties which will aggregate this data across multiple businesses.
It's interesting that it has taken this long to be commercially viable. I have an acquaintance who worked on visual perception and circa 2001 this was a hot research topic for them. IIRC, their team demonstrated a two camera system for gait recognition to LLNL around then.
