If the system relies on tracking you constantly from the moment you enter they'll have as many cameras as they need to cover the whole store. For just tracking the person you really don't need too high of detail just decent coverage and if the system is using CV to determine what you're taking off the shelves instead of RFID(ish) tags (which makes sense given the cost of applying tags to every item) then they've already got way better camera coverage than they need to just track you around the store.
Really this whole thread is all just rank speculation that'll be mostly confirmed or denied once a store actually opens and people can look around and see what's going on.
Also as for scaling it's a fixed cost to cover a larger area compared with a variable cost if they're using RFID to scan when you pass through the turnstiles so really a camera based system probably scales better than a tag based system.