It's pretty obvious they're intending the discussion to happen on mailing lists.

    We’d love to hear what UA vendors, web developers, and users think. Thanks for reading! We are discussing the proposal on web standards mailing lists:
    public-webappsec@w3.org
    blink-dev@chromium.org
    security-dev@chromium.org
    dev-security@lists.mozilla.org

You make it sound like they're eschewing discussion.