What a cool design idea...I've always loved flying sea creatures; like whales, which you see a lot in fantasy worlds. I think it's a clever design choice because the sea and air are both vast stretches of space and the creatures that reside in both have similar attributes (like wings vs flippers, etc.)
I'm not sold on the overuse of chroma grain in the atmosphere, it makes it look like a cheap digicam, like a phone camera. Luma grain with a tiny amount of chroma grain would have given it a more cinematic feel. (Especially is the chroma is mostly blue and green, with virtually no red added.)
But damn, I can't wait until propulsion is cheap enough to build one of those suckers. Gorgeous!