Flametongue is a pretty boring flat damage increase, and unleashing it is a minor bump in damage that's mostly not worth the gcd. Then unleashed fury is just a little bit more of a bump.
Frostbrand on the other hand, beefs up a frost shock snare and gives a mini sprint with UF.
If Ele could put Frostbrand on their offhand, not only would it give UE a decent use for them, but it would make UF a viable choice.
Also, an idea for a defensive for ele and enhance to try to deter mongoloid trains, a super lightning shield cd. For x seconds several lightning orbs go crazy around you reflecting the damage you take back to attackers. Nuking a shaman with this cd up effective nukes yourself too.