So, Java has 140 million people with a density of about 1 100 people/km2. Sumatra meanwhile has about 90 people/km2, Borneo about 26, and New Guinea about 14. If those other islands had Java's population we'd be looking at almost 900 million New Guineans, somewhat over 800 million Borneans, and 500 million Sumatrans. I suspect that Java is probably an importer of food from the other islands, so equal densities would be unlikely (the density it after all twice that of Honshu in Japan and only really matched by Bangladesh as full countries of significant population go). However even half that density (in line with South Korea or Taiwan) would easily give a population over a billion and rivaling China or India across the Archipelago. Is such a thing possible with an old enough PoD, or are most of the islands involved just not suit to that level of density by way of soil or climate?