I recently received an infographic from the SSL provider SSLs.com suggesting that the future of the iPhone (and by extension other smartphones) will follow a growth curve based upon the product category's first decade.
As tempting as it is to forecast the future based upon the past, technology seldom follows a linear path, for two reasons.
First, product categories eventually reach their optimum utility after which improvements provide diminishing returns.
For example, today's digital clock radios are virtually identical to those of 30 years ago. Yes, there are some models that connect to the so-called Internet of Things but such "innovations" add complexity with little added usefulness. All you really expect from such a device is to be woken up in time to get to work.
Second, new product categories sometimes jump "out of nowhere" to replace or supplant older technologies.
The smartphone itself is an example of this. The previous assumption in high tech was that mobile computing would be tiny PCs (aka Personal Digital Assistants or PDAs), hence Microsoft's (finally abandoned and ill-fated) attempt to cram the Windows operating system onto a handheld.
While PCs have obviously not disappeared, the most popular tablets are more like big smartphones than small PCs (Microsoft's Surface being the exception). This transformation blindsided PC manufacturers like Dell, who've remained largely buttonholed on the desktop and laptop.
Another problem with projecting past tech into the future tech is Moore's law, which may be approaching the point where as-yet-unidentified technology will be required to continue the pace of miniaturization.
Today's chips have components that are 10 nanometers, which is roughly the length of 20 carbon atoms. The theoretic limit of current technology is apparently 3 atoms, which is only two generations away and likely to be achieved long before a putative iPhone XL would come into existence.
Of course, there could be future breakthroughs, like quantum computing, that would either keep Moore's Law in play or render it meaningless. However, any forecast that crutches on a technological breakthrough that hasn't happened is akin to magical thinking.
There's a larger assumption, though, that's built into the predictions of the smartphone's future: the continuation of modern civilization.
While I'm far from an alarmist, at this point the only thing preventing immediate global thermonuclear war is the emotional restraint of a couple of tantrum-throwing baby-men with weird hairdos.
Therefore, a possible--even likely--future of the smartphone is: