Hey Yak, there's one thing I hope to get some clarification on. There will still be numerous pockets of water in these areas, right? Lakes, ponds, rivers, subzones, etc.? Because while I do understand you're going for a very strong 'underwater brought to the surface' feeling, there would naturally be craters, valleys, and what have you that act as little water preserves.
It'd be a way to give us at least some underwater content while also showing some of the ecologies and cultures in their natural environment.
Just a thought! It sounds like you're already planning on that, but I just wanted to have it clarified.