The only way I'd want them to introduce a 5.1-inch phone is if they could fit it into the same size frame to completely replace the current 4.7-inch.
It's hard enough getting the launch day phone you want due to 5 different colors & 3 different sizes spread across 2 different models. The last thing we need is
another model clogging up the supply chain making it
even harder to get the model you want on launch day...