Hi,
To a certain, lesser, extent this has always been the case: for example, I
filed [1] a long time ago because you can't write your own GtkContainer
subclass with an internal layout manager and have gtk_container_add() and
gtk_container_remove() still work on it, although GtkAssistant does this
Gtk+ used to support custom widgets. Whenever you were unhappy with
the official
set you would hack up your own. More often than not, this would start
by copying
an official widget's code and do a mass rename of identifiers.
No more.
More and more of the api needed to created widgets is migrate