It's a really weird question in fact. How much do you need to change a program that works in a traditional Gnome desktop (even ignoring the fact Gnome has moved on too) so that it integrates seamlessly with Unity?
My best guess is "nothing at all". Am I that wrong?
Are the people complaining about investing man-hours in extender development really developing desktop apps for Gnome/Unity?
It's very hard to balance the needs of the commercial department and the development department.