All the above are requirements, yes (CPU, Screen, RAM, Storage, Battery, Camera). I'd add one more requirement: manufacturers should be required to supply as a part of an extended warranty the latest release of Android. No more orphaning year-old phones.
Once that's squared away, then I imagine manufacturers could compete on features -- things that customers want. Here are some examples:
* Battery life. User-serviceable battery.
* Removable storage
* Wireless charging
* Multiple SIM slots (popular in Japan)
* FM Radio (popular in Japan)
As you can imagine, a phone with all the above would be pretty large, but it turns out customers like a large phone. Sadly, no such phone exists today.
Try the 3D touch on the iPhone.
Adding what is the equivalent of contextual menus to the UI is a major improvement to the overall experience and I know I will be upgrading to the 6s purely because of this.
3D Touch is about how much force you use, not how long you touch for.
* 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.