I never really bought into runners, except for short distances:
I have this concept where David Attenborough from a relatively untouched UK travels to the US to feature a nature documentary on zombie ecology. To him zombification is a return to cold-bloodedness like reptiles.
His astonishing find is that zombies actually eat less
while dead than when alive, and can go longer without eating--making zombies less a strain on the environment than live humans. They go into shark like feeding frenzies, but spend most of their time in a torpor, like basking crocodiles. He then down loads his own conciousness into a jack in the back of his neck (Matrix style) and allows himself to be bitten. He describes what it is like to turn into a zombie, with his genius intact. He speaks out of a radio collar, and is along for the ride now--the zombie in full control of his locomotion, but still has to worry about head shots.
Having David on The Walking Dead would be perfect. You would do an episode like MASH where you actually don't see our heros close up--only in the distance. You have them split up, and killed one by one. (wheather they were slated by Comic or script to die or not.
That way, if the network pulls the plug early, you insert this story to wrap things up at least. Otherwise it becomes a dream sequence.
Now to me the zombie hordes in WWZ are beyond even running zombies. To see how they spill over each other, it is almost like looking at a nuée ardente, a pyroclastic flow charging at you--a powder avalanche. These would be supernatural zombies to do that at speed, although perhaps having them look like ants, bridging gaps with their own bodies, forming living towers and battering rams would be interesting.