Add a rule for instamining deepslate like you can with stone, eff 5 diamind/netherite pickaxe, and haste 2 beacon.
Balance it a bit by requiring a netherite pick instead of a diamond pick.

There's a scarpet app which adds this. If you're in the carpet discord you can ask there.

Yes, survival/instamine_deepslate.sc (/script download survival/instamine_deepslate.sc or manual from https://github.com/gnembon/scarpet/blob/master/programs/survival/instamine_deepslate.sc)