I kinda like the Knockdown property idea.
I think I'd make it
Whip
Light Weapon
1d4 19-20 x2: Slashing
Special: On Vorpal effect Knockdown
To go with this I'd like to see Spiked Chains as well
Those I'd make
Chain, Spiked
Two Handed Weapon
2d4 20 x3: Piercing
Special: Improved Glancing Blows: Slightly Higher Damage, Proc Rate (I assume we'll eventually see Glancing Blows have a Proc Rate anyway) and chance to Proc Special Enhancements.
Kamas I'd like to see a special ability added as well.
Kama
Light/Monk Weapon
1d6 20x2: Slashing
Special: Bleeding: On critical target suffers Bleed damage 1d4 + attacker Wis modifier every 2 sec for 6 sec.
Shuriken I'd like to see
Shuriken
Thrown/Monk
1d2 20x2: Slashing and Piercing
Special: While throwing shuriken there is a 20% chance to throw an extra on any given attack. Shuriken expertise stacks with this benefit.
Exotic weapons should have something interesting about them.
Aesop