My initial goal was to maintain compatibility with very early Gtk2 releases in order to make it easier to get Gtk3 support into opencv 3.0 if possible by minimizing the risk of breaking older code. However, during migrating the code it became obvious to me that removing support for versions of Gtk older than 2.24 would allow me to simplify the code and make it easier to maintain. If it acceptable to the maintainers to only support versions of Gtk 2.24 and later then I will eagerly do so.