As part of the next release I wanted to be able to have gnome-mplayer be able to be compiled against GTK3. Since GMTK is the core of the next release, I needed to port it first. It only took about an hour to complete the work. gnome-mplayer will take more time to convert, but it should be something I should be able to do in a few hours.
GTMK running under GTK3
So I need to finalize 1.0.3 and then on to this work. It appears that GTK3 may not be able to be ported to Windows, because of the embedding in GTK3 being X specific.