Well, if the lower base ISO means a substantial improvement in dynamic range, there will be those who want it. It is a way for Nikon to compete with medium format.
Personally I use the ISO 64 quite often on the D810, and find it works great in combination with M-UP and EFCS on tripod. Also for sunlight summer event photography outdoors, it gives extra flexibility in dealing with high contrast lighting. However, I don't think ISO 25 is for me personally.
I shot a little Kodachrome 25 and Ektar 25 and felt those materials were impractical. But on a ISO 25 base ISO digital camera it is a different situation as one can adjust the ISO when needed and there is a large range of flexibility. Also it is easier to check if things are working or if there is vibration or other source of blur.
I personally think ISO 64 is a good practical compromise for base ISO, it gives the D810 an edge in certain applications. However, a lot of the time even in landscape photography I may need to increase the ISO to 200 or 400, e.g., when photographing floating ice sheets. With digital you don't have to be "locked in" at the base ISO setting.
What I really want to see in the D810's successor is Multi-CAM 20k from the D5. This AF system is excellent. I just shot an outdoor event with the 105/1.4 and even though it involved moving subjects and low light, I had an extremely low rate of out of focus shots, and excellent image quality. Now, I would like to see a low to medium ISO optimized camera with this autofocus system.