I'm guessing finishing Classic with every character, as far as the stream is going. I would argue that it's the kind of method you use to unlock the "last" character, but... heh.^ I would like to see it happen before anything honestly. Two points of confirmation is better then one. Also do we KNOW what the unlock condition is for ROB?
I definitely hope we're wrong and that guy is a masterful troll, but really, chances are becoming slimmer by the minute.