While I have no strong feelings about this, I imagine that if that's a real script (how likely is that, really?), many people wouldn't be so happy about Bieber actually nabbing the role. In fact, some folk around the web seem kind of upset at the idea. But wait a second! Bieber tweeted this earlier today, too:
Could be unrelated; maybe he's just also doing some Funny or Die gag. Could be completely related, and this is the Funny or Die gag. For now I'm afraid I'll have to leave you with the possibility (however slim) that the future may hold a movie that has Ben Affleck cast as Batman, and Justin Bieber cast as Robin.
And if this does turn out to be just a prank (the most likely scenario here, I would think)—damn, Biebs. Good job at trolling the internet!