I don't think anyone is going to make a 5 inch smartphone. Even if they make one they won't be able to sell any.
The ZenTouch button on this looks great - main complaint with my Mini is not being able access Notification Center easily one handed. Unfortunately it looks to be right hand operable only…
Yes I use a powerbank on multiday backcountry trips, but it stays in my pack, not on my person and especially not in my hand.