The iPhone X has already been a major change in the structure of the phone and has enough news so that we do not see many changes in 2018. Surely next September Apple slightly updates the internal specifications of the phone but do not provide relevant changes.
These changes would arrive however in 2019
According to analyst Ming-Chi Kuo of KGI Securities, iPhone models arriving in 2019 will have an updated TrueDepth camera to be more accurate and offer more data.
In the words of Ming-Chi Kuo:
We believe that the adoption of the TrueDepth camera for 3D detection in 2017-18 will create a demand for higher capacity batteries. As of 2019, we forecast that the iPhone can adopt enhanced 3D detection features and augmented reality features, and will consume more power, further increasing the demand for large capacity batteries.
Obviously, improvements in the camera that require more effort of the CPU and improvements in augmented reality that also require more CPU is synonymous with more energy needed. Over the years Apple has been increasing the battery and optimizing it.
On the other hand, there are important jumps where a simple optimization is not enough. It will be interesting to see how Apple manages to increase the size of the battery in the size of the iPhone X.
Another possible option is that these improvements in the TrueDepth camera and augmented reality do not occur in the 5.8-inch model.
Apple could again make a Plus model with the design of the iPhone X and it would be in this where we would see the improvements as well as the consequent higher battery, as there would be space in this case.