That's an interesting theory, but honestly I also wouldn't be surprised if they added the fast moving tail after realizing that he looks too stiff.I'm running with the theorythis is just a corpse of the original Godzilla, the look definitely imitates the original Godzilla in a number of ways, but more... Corpse-ier. Then his trail is fucking huge though, AND his tail has a face, like it has eyes, a teeth, and such on the tail at the end to imply the tail has a life of its own. I think the reason it shambles so lifelessly is that this is a literal walking corpse of the original Godzilla being controlled by a parasite that's situated in its tail, and I'm betting the fact it's a walking corpse of Godzilla is playing up some major symbolism here.
But anyway, the questionable design aside, tonally it looks exactly like what I hoped Godzilla 2014 would be.