Welp. someone finally did it. Even though many thought it was impossible, some crazy geniuses figured it out.
A no-mods, no-command-blocks, redstone-only Automatic Tunnel Bore machine
Set it off and a series of sticky pistons, slime blocks, and redstone blocks inchworm their way down the tunnel, grab the stone, and bring it back to the control room. There, separate slime block machines collect the stone from the drill head, put it all into a conveyor, and push it in to a room containing a Wither. Using snowballs, the Wither is goaded into destroying the blocks the conveyor pushes, dropping them in to hoppers to be sent along to chests. And the best part is, anytime the drill runs into a malfunction and stops working, they have a beacon that changes colors, so even when they're far away above ground, they can be alerted that the drill is broken. It's insane.