If they made it that big it'd no longer be portable. For something to be useful as a tablet you need to be able to hold it with two hands.
And no, it's unlikely the official name will be iPad Max, but it's amusing to call it that. It's a simpler way to refer to it than "bigger size iPad" or some such clunky description.
How is a 12.9" tablet portable either? I think this would be better as a powerful, touchscreen device that can be moved, but not be used in the same portable ways as an iPad.