Apple are stuck if they do or they don't.
It's ironic that they're going to go for a bigger form factor, when they decried the trend and stated 3.5" was best, and then 4", for single handed use.
I think Nokia is spot on with their 4.5" devices! I'm typing this on the lumia 625 (4.7" display) and understand that the 1520 serves a sector of the market - i have one just for gaming, movies and the like - but the truth is that larger phones are still in the minority, when it comes to sales.
Apple do need a larger phone - i just hope they stick to their ergonomic integrity and create something in the 4.5" region. They have the iPad mini for the phablet space.
Doing something because everyone else is doing it is not a good business model to follow.