Looks like the Blu/DVD will be unrated or at the very least an R rated cut;
"Forster also confirms to Focus that World War Z will have a harder version on DVD/BD because the PG-13 rating in the US was a problem that limited the things they could show. And as one of our colleagues could already confirm, the theatrical version basically doesn't have any blood. That's unusual for a zombie movie but according to Forster, that is about to change once the DVD/BD gets released."
Source - Movie-Censorship.com