So my suggestion would be to expand the underwater world of Cahaya a bit more, for example more coral reefs and more sunken objects, maybe a sunken city ruin that you could then explore with the diving ability.
Generally, I think it would be great if we could dive freely. Simply more underwater animals so that the underwater experience becomes even more realistic.
Overall, I think Cahaya is really great, also in terms of atmosphere and setting, it could just be more lively on the streets with more NPCs doing some kind of action so that the city and the resort feel more alive.