Apparently, there has been some (unsurprising) feedback regarding the matter, especially since the last Gnome version came out, concerning the lack of consistency with client-side decorations.
Just to remind you of the current (Gnome 3.10) situation, where you can supposedly set the property of whether application’s windows show maximize and minimize buttons or not by default, through Gnome-tweak-tool. These preferences doesn’t affect some default Gnome apps such as Nautilus file browser, Gedit, and some others.
Hence, Matthias has now remade the configuration mechanism which will allow implementation of the property in all Gnome environment’s apps, plus it will also allow distribution makers and users to select the side and placement-order of the buttons.
When will it happen
According to Matthias, “hopefully soon”. Currently this is still under experimental stage, and Matthias also doesn’t neglects to say that even if it would work flawlessly and all bugs will be sorted, the last word will still belong to the application developers / designers themselves:
“But application developers / designers have the last word: they can hardcode the property to just show a close button on the left, if the application design does not accommodate wild variations in the header bar layout…”