That is a very good question. I can't speak about the opinions of other physicists as to the validity of this particular theory, but what I can tell you is that there are many, many theories that try to unify gravity and electromagnetism. And there are many, many theories that predict more than the 4 dimensions we know of. Unfortunately, none of these theories yet have experimental evidence to back them up. But that doesn't mean people aren't looking for them. There are many experiments running right now aimed at figuring this thing out. Here is an interesting video that might help you learn more: