Idea I had with creature size. There's already a random creature size mod. But I was thinking more structured to show a sort of growth cycle in Subnautica. Currently every creature is the same size (I believe). For this mod I'm thinking of changing the size slightly between each species, for example say a peeper spawns as size 6, well the mod could make it so they spawn between size 3-6 to show juvenile and adult fish. Same for everything else, including leviathans (although this may affect attack animations).
This mod could make it seem like there was a growth cycle in the world rather than everything just being a default 'adult' size.