Black did hint at a possible detective story. I wouldn't think of Franco for the lead in something like the first Predator but something a little less 80s action, I can see him in. I think this comes with the same sigma that McBride's casting did, and that's that Franco is a largely known for comedy.
Franco has some other great things. I loved him Rise of Planet of the Apes. I think it's important to remember that if this is legit (and considering the source, I wouldn't think it wouldn't be) then it's the agency that is pushing Franco, not him being Black's choice.