Does it need to be lightning related? I know in lore and all why they did that, but considering Odin is carrying around a (far better looking) Gungnir, I'm tempted to ignore that completely and say ours is a phony.
I'd rather see +Critical Hit damage (though I guess that can loosely be related to lightning) which would certainly be nice for Jumps. Though unless Geirskogul suddenly stops having an AGI modifier I'd still hate SE, regardless of what they do.

Also, would an additional effect like En-thunder even work? Wouldn't "Additional effect: Defense down" block or be blocked by that? I seem to remember two additional effect conflicting when they added Grips (Platinum grip and Mezraq, only ever had Stun and never Evasion down proc), though since the aftermath is only temporary I guess that might not be much of an issue.