I get the sense that it'll be more convenient to add this after updating to 1.13, but I'll just put it down here.

Vanilla has coral reef kinds of things now but what I was thinking for this was more individual, sparse, almost tree-like formations of mire or deep water coral blocks that generate in Deep Waters. They would sort of emulate the base shape of the coral itself but could have variations, and the smaller corals would also generate on them. I thought it would be a good way to integrate the coral blocks better in the mod and it would also help to spruce up the Deep Waters biome.