Actually, the Islamists would made a Caliphate already if there is a chaos like that.
Alliances of Religious and the Seculars.
Jakarta would be a mega-city that spans from the West Java until, eh, Central? If there is no effective transmigration policy by the previouses government, Java would be full already, and food would have been growed in the outer islands.
Also, global warming would take a toll, and Indonesian's landmass would shrink. (and there will be NO way to support a half billion people. Except if they have managed to fill EVERY islands and the Malayans manages to successfully invade Papua... AND BEYOND. Or if the global warming has been stopped.)
Of course, the dissidents from the previous stable governments WILL already have a strong grip on the rural community. There would be those who stay faithful to the Pancasila, those who proclaim their pan-Islamism, those who wants power and wealth for them selves, and those who can't, or won't care. They just want to survive.
I'd say the Sumatra would be overran with Islamists already. Kalimantan... Perhaps. However, Java would be the most secular region in there. Sulawesi... I can't model about that. Bali, if the previous governments are corp-friendly NEO LIBERALISTS PUPPETS, would have been sold lend to a multi-corporation bidder. The sea would be a very contested resources, especially if there are an effective way to grow seaweeds and ... farm fishes? man-grown fishes?
Phillipinnes would have been invaded from the south already. Or perhaps it is them who invades their southern neighbours?
Islamists in Malaysia and Brunei Darussalam would made alliances with the Islamists in Indonesia already. The Arabs would support them. If they still exist as a world power, of course. Perhaps Russia would too...
If the prediction is right, Africa would have been empty (AIDS) in 2035. Perhaps there are re-colonization efforts in Africa?
Won't American Empire would be destroyed by 2035 already? The strongest powers would be EU, Brazilian Empire (South America), India (They would try to have South East Asia as their reign of influence), and China (same as India). Perhaps Russia. Or the New America. Or the re-colonized Africa. Canada?
Of course, if the Developed nations Aqizzar talked about are America and EU, India and China would be wary of the Western's involvements in their 'backyard'.
And, the most pro-western sentiment would be in Java. The other islands, not so much. And there would be many Anti-Western pockets in Java too... However, the city-dwellers would have access to the internet, and it is them who can testimony to the world at large...
... OK, I think this post is very confusing. Kudos to you who can read this and UNDERSTAND.