On sensible distros like Mint the GTK3 version is fine, have been using it for ages. Since #1181 is not committed this could be too, it doesn't change the GTK2 support so distros that want to remain GTK2 can do so, but I am aware of some that already provide the GTK3 version and that hasn't caused a massive complaint flood and will probably work better on Wayland distros.
@b4n If I read it correctly it doesn't change the default, just select gtk3 automatically if its the ONLY GTK available?