iPad Air 3 will need to keep its name so the next one will be called the "iPad Air 3D". That way, people will think its the 3rd one and folks can be confused like they were on the iPhone 3G. People be like "I missed the second iPhone???"
There was no expectation about the naming scheme of the iPhone until the 3GS appeared, which set the stage for the "S" moniker. So, no, nobody was confused. It was the 3G version of the iPhone. Made perfect sense at the time.
However, if they did call the upcoming iPad the "3D" (they won't!), then they could follow that with the "3Ds" and totally confuse people!