I imagine most of the web dev world hadn't realized that the display module of CSS3 was only in working draft status. There are some serious improvements and equally serious issues involved with this seemingly innocuous property.
I've taken the liberty of copying a letter to the whatwg and html5wg from the css3 wg. This is informative reading and well worth your time. Don't tl;dr the message.
Sep 27 (1 day ago)
to www-style, Boris, public-cssacc, whatwg, public-html, List, Daniel
About a fortnight ago, the CSS WG published an updated Working Draft of
the CSS Display Module L3:
CSS Display describes how the CSS formatting box tree is generated from the
document element tree and defines properties that control the types of boxes
Significant changes since CSS2.1 include:
* Splitting 'display' into 'display-inside' and 'display-outside'
to independently control the layout mode inside the box and its
role in the parent formatting context, respectively.
* Adding an independent "noneness" switch that does not overwrite
the box type declaration. (This will make it way more straightforward
to dynamically show/hide content.)
* Reintroducing 'display: run-in', but with more reasonable behavior
(as in, you can better reason about it. yay!)
* Adding a 'display: contents' value that eliminates the element's
own box and brings its children up to act as children of its
* Adding a handy glossary of key terms from CSS2.1 chapter 9.
Significant changes since the previous draft are listed at:
We have a couple of key issues open that we would particularly like
A. Naming of the box-hiding-and-showing property. Please send us
suggestions for improvement! (Or comments on what you like about
the current name. We're pretty unsure atm, but want it to be
B. Run-in model: we're looking for a review by Boris Zbarsky and
also for comments on how best to handle out-of-flow elements between
run-ins that form a sequence.
C. Interaction of 'display: contents' and counter numbering:
specifically, comments from implementers about the implementability
of various options, and comments from authors about how they'd expect
the numbering to behave.
D. Figuring out an ideal interaction for the new show/hide switch
and its equivalent (the 'speak' property) from CSS Speech.
(Likely we'll make 'auto' depend on the value of 'box-suppress',
but we're open to other considerations.)
Our plan going forward is to
1. resolve all the open issues (obviously)
2. defer the longhands of 'display' to another level 
3. hopefully transition to CR in the next six months
Please send any comments to the archived www-style mailing list,
, and please, prefix the subject line with
(as I did on this message). Also, please start a new thread; don't
reply to this one.
 It was a good exercise to split them, since we now have a properly
combinatorial understanding of how the various aspects of 'display'
interact. We plan to split them out again in a future level. But
there are combinations--like table cell flex containers--to this
that are very difficult to implement atm, and we can disallow at
a syntactic level if we retain only the shorthand 'display'. (The
show/hide switch, not being a longhand of 'display', will stay
For the CSS WG,