Coral Blocks

Coral bricks, pillar, etc, with stair, slab, wall, and gate variants for each.

(Also just a quick question what is the purpose of the bone brick?)

Bone brick item is for crafting the bone bricks block AFAIK, like any other singular brick item.

At the moment we don't have any plans for coral blocks, but it may happen in the future once we've worked through everything we do plan on adding. The interesting thing we'd have to keep in mind for coral blocks is the "drying out" mechanic where if they aren't in contact with water, they die. This would mean that instead of 5 block sets, there would need to be 10, and we'd have to implement the drying out mechanics for the 5 alive sets. Depending on how we go about this, the dead sets may all look very similar, but this may be a good thing for builders (blocks with the same pattern, but slight variation).

As for the bricks, what Pythagoras said is correct - any brick block can be placed in the crafting table to turn it into 4 brick items of that material, and those 4 bricks can be crafted back into a full block. This feature currently only exists for parity with the vanilla clay brick item, however we may do more with them in the future.