I personally would like a mod such as this, but I would like it somewhat lore-friendly. This for me means that there would need to be the Sload, and possibly Maormer (although they seem to stick to their islands). For those of you who know nothing of the Sload, think Jabba the Hutt with corpse-like white skin and lamprey teeth (and undeath, necromancy is really big with the Sload). They are supposed to have huge underwater kingdoms, which would make Nirn a very scary place beneath the waves. I've dreamed about exploring a Sload nightmare-inducing city since I first heard about them. Sload also get bigger as they age. Also I would like to see Sea Serpents (mentioned many times as being abundant in Nirn's Oceans). Of coarse, these are only suggestions. I really like things I download for Elder Scrolls games to be moderately lore-friendly however. As for shark races, there's nothing in the lore that says there aren't shark people, and the ocean is a very big place.