The development of technologies tends to follow an S-Curve: they improve slowly, then quickly, and then slowly again. And at that last stage, they're really, really good. Everything has been optimised and worked out and understood, and they're fast, cheap and reliable. That's also often the point that a new architecture comes to replace them. You can see this very clearly today in devices such as Apple's new Macbook or Windows 'ultrabooks' - they've taken Intel's x86 and the mouse and window-based GUI model as far as they can go, and reached the point that everything possible has been optimised. Smartphones are probably at the point that the curve is starting to flatten - a lot has been optimised but there's still work to do, especially around cameras and battery life, and of course GPUs for VR. That curve will probably flatten out just at the point that AR starts to start shipping.