Having said that, I get your point of the current Indonesian civ being mostly Javanese.
For me it's even better if we choose the next unique for someplace else from Indonesia, but I can understand if someone would prefer to keep them strictly Javanese
Perhaps a unique unit that was used by Majapahit itself is better.
CETBANG
Cetbang is a ship that can bombard cities from afar, using some sort of hand cannon. Majapahit ships is usually equipped with this weapon. Yes, gunpowder was used by Majapahit, though the quality is still bad. The weapon itself is made of pure bronze, unlike the European version that already known metallurgy at that time. It could replace Galleass, and have more ranged attack strength. One of the Cetbang is a collection of the Metropolitan Museum of Art in New York (see the link)
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layar tanjaq is also utilized in Javanese Jung, I think.
For more information regarding the differences between Chinese Junk and Javanese Junk, I think another Indonesian that write this post (also in CFC) explain my point better. They had plan to create Indonesian civilization but cancelled (probably because BNW is released?) They had already create Indonesian icon (which is more accurate than Firaxis') and Sukritact also already create Candi icon as well.