According to Hong Kong Disneyland Main Street Gazette's update, work is about to begin in Fantasyland on the "non-ride attraction". The work area is now surrounded by boards and it is indicated in the above map, near Fantasyland Train Station, Dumbo and PhiharMagic. Pixie Hollow has moved to a location near Adventureland.
So now we know the "non-ride attraction" is not the castle walk-through.
What is it though?