Accurate retinal scanning/face scanning to check where you're looking on a screen will start off being a “fun” feature unrelated to ads. Like the new emoji thing on the iPhone X that lets you control them with your facial expressions or Snapchat filters.

Maybe Apple or Google will add it as an optional feature to their alarm apps “to make sure you’re awake” or to their cameras to help “take the perfect selfie every time.” [Update: just under a month after I wrote this google did exactly that with this app thanks to /u/napolux for sending me the link.]

Maybe some game and app developers will make use of the function and people won’t mind. Pretty soon Google will integrate it into YouTube “so you don’t miss a moment and can pause videos with ease.”

Google and Apple will then create an opt-in feature for the scanning to help “improve performance.” Soon that’ll move to the small print in the terms and conditions.

Then one company or charity will approach Google and ask if they can make a skippable YouTube ad using the tech. The ad will be powerful, effective or funny. Most people will love it or not mind “I mean it’s skippable so who cares.” There will be some naysayers on Reddit who’ll point out the slippery slope.

Then someone will post it to r/videos and r/hailcorporate will complain. Some people will call it creepy and link to comments from other subs pointing to the dangers. Other people would say it looks cool. The ad would be written about in newspapers and talked about in the media. Tech sites will call it “an innovative approach to advertising.”

A couple podcasts will do episodes about the tech highlighting its problems. At the same time a couple news outlets will write headlines like “COULD YOUR PHONE BE SPYING ON YOU OR YOUR KIDS?” and someone will write a fascinating long-form article - probably in a left-leaning paper or possibly on medium or a popular blog.

Soon other apps will integrate the functionality particularly Facebook and Twitter. Not to sell adverts yet just to “optimise the algorithm to give you the content you like.” u/spez will make a post about how he wants to add it to the Reddit app. He’ll get downvoted and people will be angry. Eventually he’ll do it anyway.

Then Google and the social media companies will offer ad companies, “content creators,” and media organisations access to their “premium tier ad service” that will allow them to initially just monitor how people respond to their content. Later they’ll be able to use the tech to advertise and when people start complaining it’ll be too late. Soon we'll be flooded with unskippable ads that monitor our behaviour and expressions.

The business model will be too profitable and we’ll roll over and accept it.