Photos have never been any one particular aspect ratio. They are 4x5, 4x3, 3x2, 5x7, square, 16x9, 2.35x1, etc, etc. There is no such thing as a one master ratio for photos.
Yes, there are cameras that take widescreen photos natively.
Yes, there are apps that will do it, it just takes a little longer to fire them up than the Camera app with a simple swipe up from the lock screen.
I do not understand why Apple who, of all companies, have stampeded toward convergence of all things in their universe, have not put a wide screen sensor in their phones yet, or at least allowed it easily through software. They advertise AirPlay like there's no tomorrow, but when you stream photos to your now ubiquitous 16x9 HD television, they don't fill up the screen. I'm a child of the 60's so I know the value of printed photos, but current amateur photographers seem to prefer viewing on TV's and computer screens more. And let's face it, that is much more convenient anyway.
I think this will be another one of those "innovations" that comes with iPhone 6s or 7 that we never knew we needed until it was provided to us from on high.
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I get what you're saying, but think. How could you possibly change the aspect ratio prior to shooting? The sensor is a physical device. It can't be changed on the fly, so you're either taking pixels out before saving the shot or after. Perhaps there is a camera app that displays various framing guides. That might help.
I think you should be able to set the aspect ratio prior to taking the photos. If you are taking photos and you know that the intent is to display them on a widescreen TV, wouldn't it be far simpler to set that in advance, rather than going back and manually cropping all 72 pictures you took that day and want to show your friends when you get home?