Underground more resistant block...

After the update aquatic mining underground has become pretty useless as you can obtain many of those items in shipwrecks and buried treasure.
My idea is that there should be a new block like obsidian but more resistant. (It could require a new type of pickaxe maybe).
The reason for this is that after you get a really good diamond pickaxe with enchantments you can easily break obsidian. As well as the fact that there should be a block with you can contain the wither, as it can break obsidian. Adding this block near the bottom of the world, on top of bedrock would give a reason to mine underground to get a really strong block.
I would really like it if this could be added to their 1.14 update if it's possible.