No need to wait 10 years, you've just described what we have now. Sure, it'll be worse in 10 years, but what we have now is already so simple that toddlers do use smartphones.
What's infuriating is that there is no pro- or power-user version. I'd pay AU$1200 for the device you described above but not for a flagship smartphone from Gooapple.
I think we've conflated user desires in things like the iphone as the clever marketing from Apple Inc. I think the effect of their marketing really eclipsed the quality and features of their product line and we've drawn a false equivalency that the methodology of their product line is what consumers actually want.
I have no empirical evidence to support this wacky theory however and I remiss that it's likely 80% wishful thinking.
If we didn't have this current culture and the older style continued, this mobile phone would have a physical slide out keyboard.
There may have been a physical scroll wheel on the side of the phone that could go through programs, scroll this page And do volume - not just that.
Maybe even buttons on the back of the phone like on the PlayStation controller to take selfies, dim the screen... If the phone was dropped, the replaceable industry standard battery would eject to absorb the impact. Cracked screens would be even more rare on top of that because the device would be a durable absorbent plastic.
The interface itself would have global text and keyword search, the color scheme would change at night, There'd be an sd slot and a dual band gsm/cdma chip etc...
I look at the trajectory we are currently on and I'm envisioning everything to be a toddlers interface in 10 years that's enormously infuriating and useless where you're cattle prodded into doing some very precisely planned flows with intentionally no room for deviation.
Nothing stupid is off the table. Replace the url input box in a web browser with a "share" button to post it on Facebook or Twitter? Google nagging you about new results to some random search from last week? News sites using third party cookies to only present articles on the front page that agree with your biases? A merging of sms and email so you have no idea how things are being sent?
I can see these happening in the Name of Design.