Of course, this technology is not ready yet. Gathering brain images isn't as trivial as turning on a light switch. But imagine if it was? Most stores would install a brain reading image at the entrance of their store. They could store crucial information about our shopping experience as we leave the store. Our mood as we enter it. The amount of information that can be gathered is astounding.
Remember "Minority Report", where the ads were displayed as scanners read Tom Cruise's eyes? That might be a reality some day.

Legal, ethical and moral issues aside (although there are many), technologies such as these would exacerbate the growing issues between consumers and producers. Consumers already feel bombarded with advertising, where every inch of space is being maximized for publicity as part of some campaign. Something to consider is that when introducing such a technology in the market, what's in it for the consumer? And don't say improved service - because that usually considered more of a right rather than a benefit. If there any additional advantages for a consumer, it would make it easier to adopt. Until then, all this technology would seem to satisfy is some marketer's wet dream.