I don't play any pingers in the sideboard because all the good pingers are expensive, and Grim Lavamancer isn't what you want in Threshold. I also like that a lot of cheap sweepers deal more than 1 damage, as killing Deathrite Shamans and opposing Delvers is paramount. I love a split of Rough/Tumble and Sudden Demise as sweepers of choice. I find Rough/Tumble and Sudden Demise to be excellent in the deck as mass removal. I love Sudden Demise because it can kill flying creatures, which Rough/Tumble cannot, and it can deal with Leovold and all his buddies without even targeting the opponent.

My current removal suite:
4 Lightning Bolt
1 Dismember
1 Forked Bolt
1 Chain Lightning

I feel like Chain Lightning as the 7th removal spell is excellent. It acts as another Lightning bolt at sorcery speed which is fine honestly. You play a lot of your removal at sorcery speed anyway because you don't want to tap out, especially when your opponent has an exposed fetchland, so you wait to untap. Chain Lightning plays very well to the aggressive side of the deck, being another burn spell that can go to the face, thus giving you more reach in the late game.