Electric-types are actually kind of horrible.
Grass-types are insanely common and resist Electric-types. Dragon-types resist Electric-types. And it resists itself. Plus average HP for Electric-types is 62, average Def is 66, average SpD is 72. They're pretty fragile.
I also think Thunder is mediocre if it isn't used on a Rain team and Zap Cannon has terrible accuracy, but Thunderbolt is pretty legit. Stun Spore is better than Thunder Wave though, because Thunder Wave can't hit Ground-types while Stun Spore can.
Anyway, I don't think a new type is really necessary and it seems like it'd be too strenuous to add at this point, plus our current typing system is already very balanced.
While Grass-types have the most weaknesses, they also hurt a LOT of Pokemon that are dual-typed (Ground/Rock, Water/Ground). It's balanced.
Another type would throw it off, I think it's fine as it is and the only reason I think people want a new type is because they're bored of the current types, and we were sort of taunted with the whole idea that they can throw in types because of Dark-types and Steel-types in Generation II.