For some reason, others strongly believe this is what the new iPhone will be labeled with this "Pro" moniker terminology. It Likely won't be, because it's a Phone. Last year, before the iPhone 7 launched, it was consistently discussed/Predicted the new iPhone would be labeled Pro or Editon, and that never happened either. Not everything Gruber says is accurate, that's for sure.
The numbering system is something Apple has followed suit over the years and I'm still leaning it's a possibility, but perhaps with this major revamp OLED model, it could have a different title associated to separate it from the lower tier models. An example would be the 'iPhone SE', it had no numbering system and Phil Schiller stated it was labeled "Special Edition" later on in an interview. But it made sense why it didn't use a number in this specific instance and it was a stand alone model from the numbered iPhones.
I will say this, IF Apple decides to use a name for the OLED model, leave it to Apple's marketing team to fabricate a title that will likely fit perfectly for this model, because that's what they do so well.