The gestures support is one of the big GTK+ 3.14 features due out this September, but that's not the only big ticket item. Landing into the GTK+ code-base recently has been the new GtkInspector for better GTK+ debugging capabilities and based on GtkParasite. Another change planned for GTK+ 3.14 is making Adwaita the default GTK theme.
The GTK+ 3.14 release is also deprecating the GtkMisc, GtkAlignment, GtkArrow, and GdkColor interfaces. GTK+ 3.14 will also have CSS icons support, popover menu extensions, outside shadows support, improvements to the Windows theme, and other changes.
Other big items on the GTK+ road-map going forward but not necessarily for the GTK+ 3.14 release is improving the cross-platform support, address missing widgets for GNOME HIG compliance and Elementary apps, scene graph support, better development documentation, better integration with GLADE, and clean-ups / prep work for the ultimate GTK+ 4.0 release in the future.
These GTK+ road-map items can be found via this post by Matthias Clasen earlier in the month and the GNOME.org Wiki.