GCCreationHandler is to be integrated with Balance Box and Baby Wordprocessor. A working example of it (the way integration is done) can be seen in the activity piano_composition.
I guess we'll then be done with the task https://phabricator.kde.org/T1497 and it could be marked as "resolved" after this task is over.

For Baby Wordprocessor, little modification can be done in the creation handler if we want to implement it the way @bcoudoin had wished in the link mentioned above.