Knockback is often a lot more trouble than it is worth, especially if you are using abilities that scale damage or such from knockback. It would be nice to have an item to convert knockback into something else.
#Would like item that cancels / converts knockback
jaunty roost
rancid quarry
an item that reverses knockback would need something to compensate for the potential danger it puts you in.... 
but i like the idea
sleek quartz
You pretty much always have full agency over how much knockback you're doing to the enemies. So idk what you're doing or building.
A vacuum inverter item sounds fun, though then people would complain about "troll item that just gets you killed wtf"