If rumors are true, the camera is now in production, its a long pipeline from beginning of production to delivery. Specifications are set 2 years in advance, and the features are set in order to meet price goals. For example, Fast FPS needs a high end shutter mechanism, and a processor / memory flow system that can move the data. In the case of 4K, they need to decide on compression, anyone can turn out highly compressed 4k video that is just a joke, but less compression is progressively more expensive.
It all depends on the price point. Components are specified to meet the price.
The firmware is one of the most difficult parts and the final part of the product. Getting all the components to play together smoothly and reliably is very difficult. Firmware for single processors and dual processors can be different, so if its a single processor camera, they cannot completely use firmware from the 1DX II, but its likely 80-95% the same. Some think this means they are suppressing features from the higher end camera, but it can also mean that the hardware will not support a feature in a reliable manner. In some cases, performance can be improved, but the designers follow the roadmap for the features and specifications. Their budgets do not allow for the extensive testing to show that better performance is possible with the hardware. One example is the firmware change to the 5D MK III to allow f/8 AF. Extensive testing was required before they released the firmware update. Users already knew it was possible based on the use of third party TC's, but possible and reliable mean two different things.
A analogy, is a automobile. Its possible to revise the computer hardware to give a engine more horsepower, but at a sacrifice in reliability. The transmission may not last long, the cooling system may be inadequate, the suspension might make the car unsafe, and the engine components, rods, pistons, bearings, are all stressed more and will fail sooner. Every part is designed to perform at a certain level and meet reliability requirements. If a designer wants to change a part of the system, lots of testing is required. That transmission might be fine with 15% more horsepower, a bigger radiator can be installed, and so on until the price jumps as well.