Apps existed even before iphone, symbian had a huge collection of java applications and were hugely popular, smartphones long existed before iphone. Iphone was just an evolution of existing smartphones at that time, what iphone brought newly to the table was a full screen capacitive touch based phone running an OS which was optimized for touch, usage of which felt natural, Nokia missed the capacitive touch revolution and relied on resistive touch for a long time and relied on the aging symbian 6 to support it.
Now smartphones evolution brought basic computing tasks to ppls pockets and hence smartphones were bound to replace PCs for ppl who dont need heavy duty computing. now pcs are pocketable already.
I don't think touch screens feel "natural". More natural than a mouse sure, but I can think of no true analogue in nature for tapping and swipping on a 2d surface.
As for replacing PCs - really that's only happening in emerging markets, where poverty prohibits possession of multiple devices. Often people are even using such phones without LTE, just free wifi. In developed markets, people have multiple devices per household, including PCs. So generally speaking its a companion device, not a replacement device.
I don't want to come off argumentative, but there are a few things I wanted to chime in on here. When the iPhone was released it didn't have any app store. It mainly took off because of its iTunes compatibility, and its fully featured browser, and as you say capacitive touch. Symbian apps were never hugely popular. One can speculate multiple valid reasons why.
Apps were certainly never considered "must have" by any phone enthusiasts back in Symbian days, nor till many years after current style smartphones took off - and that was the original point being made, that "useful and essential" isn't always immediate with new technologies, sometimes its something that "comes about over time".
I'm sure that will be the case with folding screens and AR too - the consumer uses will emerge slowly over time. indeed your bringing up things like early windows phones, blackberry and so on illustrates something often lost on people today - the slow process of refinement and evolution. That's a good topic to rambled into
We started with the "mobile phone". Those huge chunky many thousand dollar things business elites owned in the 80s. We very slowly progressed to the point where iPhone type devices are considered "must have" at a consumer level, and those technologies enabled. That process took over two decades.
Future techs like folding screens, and AR/VR, IoT, as enthusiastic as fans might be, may well follow similar curves - expensive, niche moving gradually towards affordable, consumer, useful to everyone.
Which is something perhaps people should have in mind when people spout 'consumer is everything, MSFT is wasting its time focusing on enterprise'.
We wouldn't have smartphones at all, if it weren't for enterprise buying those expensive clunky 80s phones.
Not everything is yet desireable, developed enough or cheap enough, to be a mass appeal consumer driven product.
The smartphone itself, most peoples accessable example of "consumer rules everything, focus only on consumers", went from enterprise only 80s cheezeblock, to mainstream dumb phones, to mainstream feature phones, to enterprise smartphones to consumer smartphones. It went through _two nessasary_ phases of enterprise based use, in order to become a consumer product.
Consumers didn't want to pay multiple thousands for a portable phone the size of a pound of butter, nor did they care for advanced computing features at a point where such computing hadn't evolved into what it is today.
Those steps relied on both consumers AND enterprise to enable what we have today. So even with the smartphone, really consumers DON'T rule. They only ruled when the technology had evolved enough, via enterprise to appeal to them, and catch on. Which doesn't nessasarily apply to emerging techs like IoT, VR, AR, AI, graphene screens and so on - it could easily be niche groups, ethusiasts, gamers, enterprise, the elite etc - that are the ones with the application, the interest to pony up the cash to drive the tech further and NOT mainstream consumers.