Personally I'm holding out hope that Google collectively has enough sense not to torpedo this exciting new technology by turning it into a wearable AR billboard system. While I could totally see voluntary opt-in for merchant ad displays while walking around in downtown, I'm pretty sure it would have to be voluntary.
I'm optimistic that Google realizes they aren't going to be able to get away with anything more invasive than what's considered "acceptable" behavior for a smartphone. Example: I don't have merchants sending me unsolicited SMS whenever I'm within 200 yards of their storefront.
It doesn't need to be an active system. Google could monetize the hell out of it just by showing advertisers how effective their billboards, posters, and audio commercials are in the environment through passive collection.
