You know, after some thinking, I can see how the Feral Kid as the new Max theory could be possible. I mean, Max acts rather animalistic at the start of the film, much like the kid did. And there is the music box that turns up in this film, which Max gave to the kid. But I noticed smaller details that could make the argument for the theory. For example, Max in the film has a voice that almost sounds more like the gruffly voice of the Feral Kid's adult narration. And the child Max hallucinates is apparently his daughter (while Max had a son in the first film). So, with those details in mind, maybe the Feral Kid is actually the new Max, and that he became him because he lost his family like how Max lost his, and took up the name because he went insane to the point where he couldn't be himself anymore.
Now, I know, "But how did the Feral Kid get a V8 Interceptor with the same mods when the mechanic in the first film said he had to salvage what he could find to put the car together?" After some thinking, I've got a possible explanation: the body of the car may not be as difficult to find. And in The Road Warrior, the gas tanks exploded the back of the car, so there's a very slim chance the car's engine may have still been mostly intact (I say very slim, taking not only the explosion into account, but the crash that occurred before that. The main engine block and some of the other parts for it may have survived and years later, after the Feral Kid grew up, he put together his Interceptor, long before he lost everything).
Like I said, I can't see how the theory could be possible, though unlikely.
