Thank you for point out predecessors' question!
I read the question and get some points, but I thinks the situtations change a lot and I am not ask the same question.
1. I am not ask for why GTK choose to implement in C, I know it have some historical reason. I want to make a proposal that gtk could be re-written with c++ just as GCC does. I want to discuss with you whether it is a good idea.
. Although there are gtkmm available, but gtkmm didn't gain enough official support and recommend as GTK, and much fewer reference, help, support available. The official recommand is gtk in c rather than gtkmm in c++, so many devlopers read some tutorials and feel threatened and leave. What's worse, gtkmm didn't wrapper all of the gtk featurese. In some complex cases, developers have to use the low level gobj pointer to get things done.
Now is in 2014, It can't be more normal to develop GUI application with OOP style. I think it's time to change.
GTK could be rewritten in C++,