I can't quite express how exciting this is. Not only does it make the flex module something we can use in a much more extensive way without building in clunky fallbacks, but (like with RICG images) it shows that the WordPress community can be at the forefront of the battle to push modern web standards forward.

The web community as a whole owes the 10up team a huge debt of gratitude for making this tool available to us all and paving the cowpaths for widespread use of the Flexible Box Layout Module.