The idea is for a Shaka Zulu type figure to conquer all of Papua New Guinea in 1100s and unite it. What would it mean for Papua and the rest of the Indonesian archipelago.
All of the area conquered by Shaka Zulu spoke languages from the same dialect continuum. Meanwhile, people from two adjacent valleys in New Guinea speak languages as distantly related as English and Chinese. There are barely trade routes in most of the highlands, how could you have an empire?
Given the whole place is covered in thick jungle and in addition high mountains yes. Also the social structure isn't there for such conquests and there is a lack of any effective communications.