In order to make King Ghidorah a good villain, they (the writers of the Godzilla sequel) need to give him a motive, what would that motive be? Would Ghidorah be a weapon for an alien race to take over Earth? Would he be a rogue monster that consumes the life out of what ever planet he's on? Or would he just be another prehistoric alpha predator, like Godzilla, who fights Godzilla for dominance?
If I recall correctly, his motive was summed up as him doing what he did in any given film for the evulz and because he could. It's a rather shallow motive, true, but it's still a motive. I don't see him being a weapon for anyone. He's not that easy of a beast to control and Mecha King Ghidorah was more or less a reanimated corpse with cyborg parts. A rogue monster or an ancient predator would be better suited for him. I'm leaning more towards predatory rival if they go the ancient monster route like Big G.
Aerodynamic, he was not. I watched Ghidorah The Three-Headed Monster, and I'm thinking "This is Godzilla's greatest foe?" He was kind of a joke. I just know the sequel to the 2014 movie's going to make him the badass he deserves to be.