Skill effect duration Malevolence Watcher's mod not implemented?

Hello,

Looking to get my hands on a Watcher's Eye with the "(20–30)% increased Skill Effect Duration while affected by Malevolence" mod after seeing it on poedb, I quickly realized none of the trade websites were indexing the mod. (poe.trade has it but it doesn't apply any restriction)

I wanted to check as best as I could, and did a search on the trade website for Watcher's Eye, ordered for the most recent ones and the oldest ones in Synthesis (that way it's unbiased by price), showed as many as possible and looked for Malevolence mods.

After going through over 80 Malevolence mods, I've seen every one of them, except the one that grants skill effect duration. This leads me to believe the mod hasn't been implemented yet.

Yes, can't find this. :/