The one pain point I can see coming up again and again is that the way of making something full-width isn't to specify "width:100%" but instead to use flexbox.

The one pain point I can see coming up again and again is that the way of making something full-width isn't to specify "width:100%" but instead to use flexbox. While that makes sense to me, I've already seen quite a few people (on SO for example) tripping up on this. For the rest of the properties I imagine anything that's really needed will be coming - many seem trivial to implement.