Maybe that's it? The product category of "smartphone OS" is now so well-defined that the possible improvements are evolutionary at best, not revolutionary, and hence there's also no space for a new entrant to provide a big enough improvement over the incumbents to gain significant attention?

Firefox OS promised to make app creation easier through web technologies, but "not enough apps" isn't the problem with Android or iOS, quite the contrary, so for an end user, that's pretty irrelevant.

Yeah but a year for 70 more emojis? Come on now. With all the good engineers they have.. There always must be a good idea in the span of a year..

Well, even at a tech conference, "we eBPF'd and ASLR-ized your app sandboxes even more and now you have even less risk of getting pwned" might draw a "meh" reaction. In very real terms it helps close the device security gap between Android and iOS, but it probably just can't hold people's attention.

My theory specific to iOS 10 is that it's actually a stability-focused maintenance build behind the scenes. The emoji are for cultural appeal while they hide the fact that the real features are not actually features- they're boring, hidden fixes to stabilize iOS after the previous few releases.

That's what users actually care about. Market demand.