You really don't know anything about the Penguin character, do you? Penguin is probably one of the easiest villains to put in Nolan's more realistic films. He's a high-class mobster, who's a bit overweight and has a slightly hooked nose, what's unrealistic about that? Tim Burton's Penguin was nothing like the character of the comics. He wasn't a mutant freak raised by sewer penguins (do thsoe even exist?) He was raised by his wealthy parents, and he grew up to run an organized crime ring, while also owning a nightclub called the Iceberg Lounge. That's really not that unrealistic.
On the otherhand, I rather like the rumored British arms dealer take on the Penguin. I could see Penguin as British, as it would help to explain the way he acts and dresses. Making him an arms dealer could also be an interesting way of fitting him into the story. Beisdes, it could give them a good chance to work in his umbrella gun. Since he's a weapons dealer, he could feasibly have the means to create a gun disguised as an umbrella.