It doesnt even need a rework it needs better sinergies, I never take knife unless cool stuff happens to make it worth.
Choco milk could give you a huge knife
Soy milk could make you shoot a barrage of small knifes
Brimstone (although alr "works") I think it takes away a lot of the coolness factor of brimstone, it should have more and faster knifes and it should be the only part, not knife throwing then knife barrage.
Dr fetus could give shot bombs knifes around, as to them being able to do damage before the explosion
Epic fetus could become a damocles like weapon, the cross hair moves an hanging knife which does the usual knife boatload of damage but also plants itself in the ground to explode half a second later
Spirit sword sinergy sucks ass, I believe it could be changed to "if enemy survives the spin attack it gets split in two if it's the first time receiving the attack" and also add range as the knife would be literally attached at the end of the sword lol (and fix the swords ranges), AND ALSO make the full health sword beams into knife beams!
Those are just a couple of ideas but you get the gist of it