I believe for unification, in Luzon, there must be simple tech like wheel, the field engineering absent in precolonial times. Most of these tech in OTL were brought by the Spanish.
So we need an earlier and deeper Chinese involvement.
Unification in Visayas means some sort of a navy, thassalocracy.
How about stronger links with Polynesians?
In Mindanao, population with a sense of rationality. And the Moros wont be able to unify Mindanao until they actually culturally change/mature like the Vikings and move away from piracy/raiding and treat their neighbors as vassals rather something to pluck from and discard. My prediction is if the Moros dont change, they will end up far worse in OTL where a Hindu/Buddhist or Pagan state will eradicate them from existence and then unify Mindanao.
Or maybe they become assimilated later on.
The Chinese must actually bring their civilization to the Luzon not just trade which includes these simple tech. Absent of these simple techs including cultural/social maturity, there is no chance to unify those three major islands.
I agree.