As an interesting idea, I'd thought we focus on something such as the following:
Indonesia, unlike it's chaotic neighbor to the north, of China. Has prospered in the past two hundred and fifty years. The Uthong dynasty of the Ayutthaya has risen in power steadily, and after nearly two hundred years of war, they have succeeded in the unfiication of Indonesia. They have fought off Muslim influences for generations, although the greatest threat to the new homogenous state is that of rebellion. The people of these conquered lands, remember a time when they were free.
King Ramesuan III rose to power in 1417, under his rule there were many measures taken to increase the various rites of the subordinated people, although he works diligently to fend off those who would seek to spread Islam among his people. He himself is a devout buddhist, although the Islamic heresy that spreads through his lands, is but one of many sparks to rebellion.
In 1419 King Ramesuan III deemed that under his rule the people of Indonesia have prospered, and that this was no longer a time for the state of Ayutthaya to be the principal name of this new 'Empire. He has declared himself Emperor of the Ramesuan Empire *Named after himself!*. He hopes that with this declaration it may sway the populace of the conquered peoples, and that he might one day see his Empire unified in more then just territorial boundaries.
Although, little did Ramesuan III know that his demise would come far sooner then anyone had expected. Emperor Ramesuan III was assassinated by his eldest son Moghabil. Moghabil wished to seize the throne for himself, because his father had deemed that his younger brother, Ramesuan IV should become Emperor after him, instead of his eldest son, who was a drunk womanizer, and largely considered to 'stupid' to rule. Thus the newly founded Ramesuan Empire was thrown into chaos!
Note: They obviously will not own the territory that formed Dai Viet. But this means that it will take a very good player to keep the Empire intact. They will start with bad sliders, and entirely decentralized government.
Anyway, what do you guys think of this idea? It starts off with a major dynastic conflict, and I already have negative events plan, where the Empire splits in two with Ramesuan IV leading a Royalist rebellion, to claim his rightful throne. This would work kind of like Bohemia. The player gets to decide which 'side' he is on.
I'm purposing a Zealous A-historical semi-unified Indo-china. Not the islands, Malacca would probably start outside the empire. This really just gets rid of Champa, Laos, Khmer, and unifies all of them under the Ramesuan Empire. *which will split in two hussite style 
