Underwater Mineshafts

So in the latest snapshots, there's just so much water to the point that we're toast when all we have is an underwater ocean. I love that idea, honestly! However, like before 1.13, these underwater caves are so bland and lame and sad, so why not add underwater Mineshafts?

They would be airtight with the help of glass and uses any of the three annoying blocks' polished versions (Andesite, Diorite, and Granite.) They would also have a different loot table focusing more on less valuable loot but more valuable aquatic resources (such as enchanted books that have something to do with water), and fricking sponges.