Next year's iPhone X2 Plus is rumored to have 6.5". It should basically be about the same height of the current Note8 which is at 6.3".
The X is to replace the 4.7" models for good and 2017 is the one time the smaller one wasn't gimped with similar battery life, same amount of RAM, higher 400 ppi, and Telephoto as the Plus model.
You could laugh at your Note8-owning arch nemesis because the phone is too tall but Apple is known to compromise the smaller one and make the bigger one the better one again.
Don't be shocked if the X2 Plus gets the most RAM and more features for Apple to charge premium no different than their iPad Pro series. Apple's mentality is BIGGER = BETTER = MORE $$$$.