People keep saying that and time and time again it's proven wrong. It has been wrong for years, and it will keep being wrong. If large phones were impossible, impractical, and undesirable, people would stop buying them. But they're not. They're demanding them in such large numbers that even Apple has put out a massive, massive phone. Even Nokia put out a massive phone. Samsung started matching the size of their flagship to the size of their largest phone years ago.
Every manufacturer has a huge phone, because the majority of the buying public wants a huge phone. But still I hear people say "big phones will never catch on". Guess what? They did catch on, and they're not big phones anymore. After several years of being big phones, they're just called phones now.
I think you're conflating several different things here. Something can be impractical but still desirable. For example, big SUVs are a pain in the ass -- they are inefficient, difficult to maneuver and hard to park. Yet people still buy them because of a simplistic "bigger is better" mindset. How many people with big SUVs actually use all the space in the vehicle? How many people with half-trucks actually use it to haul big and heavy equipment that would not fit in a smaller car?
Yes, big phones are impractical. This is simply common sense: they are difficult to fit inside pockets and impossible to use productively with one hand except maybe by Hafþór Björnsson. And yet they are desirable because "Big" is a status symbol.
On the horizon, I see a disconnect between the ideal size of mobile devices and the practicality of carrying them around everywhere. Poolside, hiking, on the toilet, out to dinner.
Something will have to change to fix this. I see the solution as new fashion trends that will be ushered in by people who are young -- young enough not to think that, for example, wearing a cell phone on a hip holster is symbolic of greybeard-ness, etc.
Male fashion will just up pocket sizes in response - my dad when he goes traveling has a jacket he can fit a 13" macbook air into.
The TV with the brightest, most overly saturated image might seem like the best choice when sitting on the shelves of Best Buy, but not the best choice overall.
Surely you agree there is an upper bound, though?
What I was specifically saying is that people here keep calling 5"-6" phones "too big" yet the mass market keeps buying them, in huge numbers. I'm not sure if you can walk into an Apple Store and pick up an iPhone 6 Plus off the shelf yet or if they're still sold out.
The people who want physical keyboards, SD cards, smaller screens, and removable batteries are not numerous enough to sell $600-$700 phones to, not with competitive specs. I live in the US and I would love a mid-size diesel truck-based SUV. Toyota even makes the 4Runner that meets those exact requirements, sold overseas. But I am massively in the minority in the US, so I Toyota won't sell me one.
It sucks, it does. But much like we don't say we have a "big screen" or "flat panel" TV anymore (now it's just a TV), a phone the same size as the iPhone, the Galaxy, the Moto X, the One M8, etc isn't really a big phone anymore. It's just a phone.
The strap idea is interesting.
I have a hard time imagining a phone that gets people who aren't already carrying purses to start doing so. In addition to the social awkwardness (man purse?) it's just so much harder to lose something that you keep directly on your person.
There's your startup idea: pants and shirts with large pockets.
Will handbags or hip bags become common for all? Will the average size of phones rebound and approach some smaller-screen equilibrium size near 5"?
Everything depends on the adoption of these devices by younger people -- whatever becomes "cool".
My prediction is that phones will become strapped to arms or shirts somehow. I see some sort of arm-hoslter or dedicated shirt pocket that comfortably, securely houses a mini-tablet.