Although I loved the idea in essence, i think it needs a lot of work.
1) Generating large amounts of mobs inside the sea would really take up the memory and that, i don't know the technical side of things but that's what I'l guess, feel free to correct me if I'm wrong.
2) I don't think that an ocean should be Jam packed with cool stuff like the overworld. I mean sure, Kelp, shoal of fish, the odd ruin (or whatever you guys want to put down there, you can't expect me to read the whole thread!) But not jam packed full of exotic fish.
I like the idea in general though. Perhaps the memory issue could be resolved by only generating mobs when you are inside the ''ocean biome (perhaps 15 blocks underwater?)
My idea: strong fishing rods. you can craft them with strong string. You can craft strong string with 1 blaze powder and 1 string. Then just simply craft a fishing rod with the strong string. The strong fishing rod will allow you to catch bigger fishes, for example sharks. Do you like the idea? What about underwater villages that would be awesome, just like villages but collapsed, make them very rare just like Atlantis :3
There should be small fish and coral at the shallow waters. It would be nice if it had some colorfull fish in the water.
The deeper water should have lots and lots of coral on the edges and there should be lots of fish like: Clown fish, Eel, Moorish Idol, Lion fish (should be poisonus), Rainbow Parrot Fish and manta ray's . But when theres prey... there's also predators. Ive been thinking and i came up with a few shark species: Great white, Nurse shark, Hamer head, Tiger shark and the Bull shark.
And finaly in the really deep water there should be Eels and some other deep sea creatures like octopus, shrimp or crab. ANd there should also be some kind of animal that is the fear of the sea... An animal that WILL f**k youre day up! That animal should be: The Megalodon.
Great white; This shark should be quite big: probably 5 blocks long and they should be rare and deal 5 hearts of damage and has 18 hearts of health
Nurse shark; non hostile Shark that won't attack if not attacked. 3 blocks long, deal a half or 1 block of damage. and has 9 hearts of health
Tiger shark; 3 or 4 block long fish that only spawns at night and that is hostile, it should deal 3 or 4 hearts of damage. 13 or 14 hearts of health
Bull shark; 3 or 4 block long shark that is verry agressive. It should deal 5 hearts of damage and have 15 or 16 health.
The Megalodon: Giant ass shark that is 10 or 12 blocks long. It should deal 7 hearts of damage but it has 50 harts of health! Note: This shark should be super super rare.
I support the idea of adding deeper oceans and spawning more materials (kelp, sponge, coral etc.) but I'm not a fan of diving suits.. seems to technologically advanced for minecraft.. I would stick to enchantments like aqua affinity or adding a water breathing enchantment.. also we have night vision potions that would be good for underwater exploration... maybe adding some sort of bioluminescent material that randomly spawned under water would be cool..... But yeah.. I support the expansion of the ocean biome
Seaweed: easily found in the ocean and used to make sushi by crafting like this:
(none) (none) (none)
(seaweed) (uncooked fish) (seaweed)
(none) (none) (none)
Gives 2 hunger points to the player (cannot poison the player)
Also have shells that sit at the bottom of the ocean on sand. When broken they will most of the time drop shells but have a rare drop of 1 pearl. The deeper you go the more the chance of dropping pearls. It would really color up reefs. The shells can be used as decoration (can be put on any block) and the pearls can be used for maybe weapons or armor. Also squids should drop meat that the player can put in a furnace and get kalamari also gives 2 food points.
These are just my ideas please fix if you see something wrong. Thank You!
I also hate the ideas of diving suits but the ocean expansion is cool.
Also the biolecent material could be gotten from anglerfish or some random mob.