4.7 inch = iPhone mini
5.5 inch = iPhone Air
Would fit with the iPad naming convention...
Or to fit with MacBooks
4.7 inch = iPhone Air
5.5 inch = iPhone Pro
But I find it hard to believe they'd move away from the numbering... But they did with the iPad I suppose.
The Macbook naming convention is not Pro and Air, it's Pro 13"/15" and Air 11"/13". The two iPhones are not two different classes of devices, so Pro and Air would not make sense. Air and Mini would be plausible, as would iPhone 4.7 and iPhone 5.5. An iPhone (or iPad) Pro would only make sense if they introduced a new class of device, for example something with an active digitizer, or all the new models (both sizes) are pros and the repackaged old model isn't. All that said, it seems like they plan on continuing with their current numbering convention for now.