Assuming good faith, the technology makes it possible for your browser, OS and hardware to attest that the website is running in a certain type of environment (e.g. not a bot/scraper) which could be trivially extended to attestations such as "No, this client isn't using an ad blocker". It takes even more control away from users by having their own hardware snitch on them.
You can reference numerous previous discussions on HN regarding WEI for more information.
They withdraw it somewhere between 2-6 weeks ago due to the reaction.
I used to work at Google, I got over the initial 'gee we're pretty nice and concerned' thing, but would like to gently point out the tendency of people to be slightly histrionic and misinformed about it. The gap between what it was, briefly, and the confidence you have in its intent and current state are quite wide. Certainly well-intentioned and appreciated, but ultimately alarmist and inaccurate.
I know the current iteration of WEI was withdrawn and I don't claim to know what their current intentions are. They might be completely innocent, but the fact is that WEI would pave the way for abuse. Once the core functionality is there, there's an obvious financial incentive for them to start expanding WEI in order to boost their advertising revenue.
These types of ideas with significant potential for abuse should be introduced with extreme caution and with at least majority agreement of everyone affected. Instead Google tried to pull a fast one and refused to engage criticisms in good faith. My response might seem alarmist at first glance, but I don't think that's a fair accusation given Google's behavior. I expect this proposal to return under a different name once everyone's forgotten about it and I hope the backlash then will be as severe as it was against WEI.
You can reference numerous previous discussions on HN regarding WEI for more information.