We usually try not to create feature-based criteria like this, so that we can actually release the software on a time-based schedule, as long as we are fairly sure that the important stuff will get done. So we don't demand that applications are accessible or internationalized immediately, as long as they can be eventually. But we have some limits – for instance, Platform APIs must be stable, not just likely to be stable some day.
The GTK+ team are 99% there. They document almost every new function, signal, and property, mark which ones are private, and when they were added. It works well. So, would any GNOME Platform maintainers rebel if the release-team said “No, you can't add that function (or add that module) until you've also written some gtk-doc documentation for it.”?