According to Hollyscoop.com, the "Hannah Montana" star reportedly "stunned" Warner execs during her audition, even dressing for the part in a "full batsuit."
“She was sort of hopping around the room and had even written some dialogue for herself," a source said of Cyrus' audition. "The problem is some people aren’t really convinced Miley has the acting chops to pull it of.”
This conflicts with everything Christopher Nolan has done thus far to establish the new Batman film franchise as something at least semi-plausible. The good news is, I don't think Nolan would ever go for this, and I'm inclined to think that it's either a) not true, or b) Warner's was trying to be nice to Ms. Cyrus and this will never come to be.
At least, I hope it will never come to be. Otherwise, Warner's execs are jsut as good as the ones at FOX that decided to bring back Futurama, only to talk about replacing the voice talent.