Grimstone instant-mine

The newest Snapshot (21w07a) introduces Grimstone, the block that generates below y=0 instead of stone. My main problem with this block is that there's no way to instant-mine it like stone (with an eff V pick and Haste II beacon). This only leaves tnt as an option to clear giant volumes of Grimstone.

My suggestion would be to make Grimstone instant-mine-able with an Efficiency V Netherite pickaxe (with Haste II), but NOT instant-mine-able with an Efficiency V Diamond pick.

This would still make Grimstone an interesting new challenge, while still keeping the option open for clearing large volumes of it in the late-game. It would also encourage players to go mining for Netherite Scrap, as at the moment the only benefit of it is a bit of extra durabillity on your pickaxe.