I would have liked to have seen mesoamericans (possibly other natives, but it's really not too relevant for any native without mesoamerican tech group) given the ability to build only trade and transport ships. There was trading going on in the Carribian, and I feel like a human should have the option of colonising the Carribian as Maya, pre-westernising. An over-the-top improvement would be a new boat, available to only Meso tech, called Cannoes. They have +1 trade power, and one transport. Zero guns, and 5 hull. Give them 5 or less speed. 5 hull makes them strong enough to be capable of running from a battle, sometimes, but 5 speed means you'd better hope the dock is close. But, they are SOMETHING.
Carracks were op for natives.