The whole point of TFA is that it doesn't matter what code the developers write; the browser needs to block on handlers regardless due to how the events are specified. The described new feature fixes this.
The point of passive listeners would be to make it easier for developers to not accidentally write shitty code and boost performance on well written code that doesn't have to be blocking the scroll.
1. https://developers.google.com/web/updates/images/2016/10/avo...
2. https://github.com/search?utf8=%E2%9C%93&q=non-passive+event...