Mozilla's vision for the MDN Product Advisory Board is to build collaboration that helps the MDN community collectively maintain MDN as the most comprehensive, complete, and trusted reference documenting the most important aspects of modern browsers and web standards.
Interesting none of them mentioned WebPlatform, the previous attempt at this that kinda fizzled out. This effort seems a little more likely to succeed as it already has a successful foundation, actual staff, and a benevolent dictator in Mozilla. It's great to see browsers complete on user features but cooperate on standards and education.
Worth a shout that we dabble in "docs" for CSS features ourselves here at CSS-Tricks with the Almanac, but if anything in there is worth taking for a unified resource like MDN, be our guest. Not to mention everything public on CodePen is MIT, and there are loads of Pens that demonstrate web features wonderfully. For instance, that's why I built this one.