I will predict Global Maximus Productions, no later than Mon 4/23, will announce Bieber to be hosting the concert in support of the movement he has been behind since May, 2011, when he signed on with PhoneGuard/OPMG.
Whether or not he belts out a song or two is another matter, but just knowing he will be there, if I am correct, will most likely sell the place out and PPV tickets will go viral.
Only a gut feel prediction and nothing more.