Somehow I get the feeling that they won't. Armchair observers opining on the internet have never felt the need to rely on data before. They've long since drawn their conclusions and simply shop for justification; freely inventing some if acceptable evidence doesn't present itself.
So no-one's mind is going to be changed, regardless.
If you were bullish and it tanks, then Apple's 'premium' segment is assumed to have already moved to ATT. If you were bearish and it takes off, then it's the usual "marketing" and "cult" arguments again. The very marks of 'tank' versus 'incremental' versus 'wild success' will be subjectively twisted all to high hell. It won't matter if Apple sells 6M or 12M.
Just watch the reactions when the inevitable avalanche of pre-orders and launch-day lines are reported. "macolyte" and "marketing circus" will get bandied about again, along with suggestions that once the early movement is cleared out then the real measuring of Apple's success on Verizon can begin...