* CPU: Processor evolution is stagnating, and processors are so powerful that they can handle most typical workloads with ease. Efficiency is now the order of the day, not raw power.
* Screen: Densities are so high it that not only does it become difficult to manufacture higher density panels, but it actually hurts the device by draining more energy and killing performance and battery life to display pixels you aren't going to see.
* RAM: 2Gb, the standard in mid-range phones and up, is sufficient for moderate use. 3Gb is comfy and 4Gb is gigantic. Again no substantial improvements in the horizon.
* Storage: The more storage the better, but phones seem to have stabilized in the 16/32/64/128Gb, and anyway with cloud storage this is less and less of a concern.
* Battery: A major pain in modern devices, with no imminent breakthrough in sight.
* Camera: Incremental upgrades are looking promising, but there's only so much you can do with optics in a small form factor.
In short, no major improvements or evolutions in the smartphone field are in the horizon, but they aren't really necessary for the short-term anyway.