Galeon has been dead upstream, and on life support in distros for a very long time. I don't think there are any real users of gtkmozembed anymore.
The javascript engine (mozjs) is still being used in a few places (most notably in GNOME Shell via gjs). But if they continue being apathetic, I guess we'll have to move to WebKit/seed.
I do wonder what effect this will have on xulrunner-dependant projects such as Songbird will they permanently fork off xulrunner?