Going out on a limb here ...
I called an end to PC sales back in 2012. So far I have been right.
I am now calling an end to smartphone sales.
Of course they will be made - and sold. But it should be blindingly obvious to anyone (who isn't trying to flog their consultancy - looking at you Gartner) that
1) everyone who wants one has one
2) any sales from this point on are
2.1) - replacements
2.2) - first handsets for newer users.
Beyond that, any *growth* will come - and only come - when the next Smartphone offers something the current crop don't.
Now that will happen - I remain convinced that the next area for innovation and development will be assistive technologies. Not because manufacturers have suddenly felt sorry for the less-able (who are still scum as far as the market goes), but because the early fanbois of the 2000s will be approaching 70 very soon, and the market can't risk them giving up the shiny because of fading eyesight, hearing, and co-ordination.
When that happens, we'll have the sales upsurge.
Here's another prediction. Any iPhone 7 will only show development in areas which can be built upon by adaptive technology.
If I am ever called on to back up my assertion about the lack of interest in the less-able, just google "Talkback bluetooth" and see the lack of coherent hits for what *should* be the blind/partially sighted persons saviour.
Unsure of what icon to use, but I'm now pretty pissed off.