This isn't the privacy and common-sense win you think it is.
I don't think you're being sincere in your concern.
Because of this, any real interaction with an email message - where the user has to interact with the content, could then be counted as an, "open". If you get any other interaction with the message - say a user clicks a URL (that is also tracked), you just look and see if an, "open" was also recorded for this message, for this user - and, if not: record an open.
You'll still get instances when opens happen in messages, that aren't tracked, since no other interaction is done - there's that inaccuracy. But, if no other interaction is done, might as not count it as an open, anyways. Perhaps we should rename, "open" track as, "was this person, at all engaged, in the slightest?"
You can also then just give that a ranking: opened, clicked x amounts of links, followed through with a sale, DIDN'T unsubscribed - good rank!
Citation? I was not aware of this.
Selling eyeballs: yes.
Selling information: oh good lord no, so very, very no. That information is never ever leaving Google's servers.
Imo it's enough to be a bad thing. We can't rely on good will of companies to fight incentives and money in the name of privacy of their users.
Even the evilest of companies isn't going to sell off its competitive edge, that's just idiotic.
Also you are wrong, Google is not a marketing company. Google is a middle man company. Google matches marketers to consumers. THAT is Google's business. Google is paid to be a match maker, nothing more.
Marketers don't care who _isn't_ reading their mail, they care how to send mail that more people will read.
Who subscribes to a direct email campaign (and doesn't unsubscribe, and doesn't flag as spam), and is still offended by the thought of the sender knowing it was read?
Those people can flip the setting back to prompt-to-show-images.