On the beta forums it was talked about but it never made it to live (I have no idea if it ever made it to Alpha even).
Monkey-grip allowed you to wield a two-handed weapons (like an ESoS) in your main-hand and either have a shield equipped or a 1-handed weapon in the off-hand. As mentioned above it never made it to live.
Thinking back on this, how OP would this have been really? We got a one-handed ESoS (Balizarde) in CiTW . . . would being able to wield an ESoS in your main-hand really have been any more over-powering especially since you'd be stuck with one ED?