There is the Kingdom of Tondo, for example: A polytheistic melting pot of a Kingdom that lasted from the 900s until 1589 and was a somewhat influential trading empire. They had relations with Ming and eventually embraced Islam around 1500 and tied themselves to Brunei. There is actually a mod out there that has quite a lot of interesting suggestions for this region, you can find it
on the forums.
I know not a lot of people play in that area so it is probably low priority, but it is a very fascinating start region for me and it always felt like it needed some more flavour - especially when the Europeans arrive.