I can't help but agree that Bieber isn't really worth the attention, and this is nonsense rumour is overblown. I think we have to acknowledge that the kid is just kinda awful, both in music and as a person by most accounts, but not worth the attention, and would suck as any Robin.
Especially Jason Todd. He's a badass, and like, one of my favourite DC characters. We say Bieber die that one time on CSI, and he wasn't very good at it then, I don't think he'd be better at it in tights.
That said, if they're going for a sort of contrast between Dark n' Gritty Nolan Batman, and something a touch more campy with Affleck Batman in this Bat VS Supes movie, I can't think of a better way to seamlessly show that contrast in-action than by involving Todd in some fashion.
Though I just like seeing the Rebel Robin in more stuff. He was excellent in Under the Red Hood (voiced by Jensen Ackles), and while Grayson contrasted Batman's serious side, Todd contrasted Bat's "pacifistic" side (Drake I haven't done much research on, nor the Batgirls and Damian) in a manner I find infinitely compelling...
...S'never gonna happen, so just lemme have this speculation window to vent.