Today's GTK+ 3.19.7 release makes use of the new Wayland DnD support that just landed today. In the Wayland scope GNOME 3.19.7 also adds support for kinetic scrolling. Details on the GTK+ kinetic scrolling can be found via this bug report.
GTK+ 3.19.7 also had Adwaita theme fixes, drawing scalability has improved for many widgets, the managed DnD support also works under X11, and there are a number of bug-fixes.
More details via the GTK+ 3.19.7 change-log. GTK+ 3.20 and GNOME 3.20 will be officially released in March.