This is not something that is limited only to X-Pro2. "Dials" play an important role for the X Series camera operation.
Especially those that manipulate the exposure, index dials are used so that "One can see the setting at a glance", "One can check the setting without turning the camera on", and "Anyone familiar with a camera operation will easily understand it".
The dials are not about being nostalgic of the old days, but rather they are in place for their practicality. The photographic expression is determined by the combination of shutter speed, aperture, and exposure. In addition to the combination, there is the ISO sensitivity play another important role. The practical operation is about being able to manipulate the 4 elements with precision.
The original X-Pro1 was able to manipulate 3 of the 4 elements with the dials. The ISO sensitivity was inside the menu. It wasn't the end of the world, but when the X-T1, a camera that had an dedicated ISO dial, was announced, then people quickly realized the significance. We started getting request to "Add the ISO dial to the next X-Pro model!"
Since its early stage of the product planning for X-Pro2, various patterns of "ISO sensitivity display" were taken into consideration.
From LCD display to ISO dial underneath the exposure compensation dial, many ideas were brought up before we landed on the final decision. The final decision was made because "One can see the setting at a glance", "One can check the setting without turning the camera on", and "Anyone familiar with a camera operation will easily understand it".
Just like landing on the final layout took some time, realizing the mechanism and manufacturing process were not easy. It may appear similar to that of a film camera, but the mechanism is completely different.
First, there are far more number of positions available in the digital era. There are 22 positions in total, quite a lot of number for an internal dial. The advancement in the high sensitivity led to the increase of the number. Secondly, the dial is electronically linked. The analog dial operation is converted digitally to know exactly what the setting is. And Lastly, this mechanism has to be weather-resistant.
In order to meet the requirement, the Shutter speed / ISO dial required 38 parts for its composition.
This number is the fourth largest after the finder, shutter unit, and mount. This is not only about number of pieces, some parts required highly tech solution to manufacture the piece.
For example, in order to achieve the accurate 22 positions, the piece needed to be very precise and durable regardless of its complicated form. This piece is realized by a method called Metal Injection Moldign (MIM). It is not cost friendly, but the this method realizes the metal part to be durable even in its complicated form.
Why do we spend so much time on this one dial? Unfortunately there is no economic and rational answer to that question. But it was something that the developing team of X-Pro camera had always dreamed of achieving. And it was also something that the passionate X-Pro users strongly wished for.