It will only pass through 4K, and would require a hardware change (Chip) to be able to upscale to 4K.
4K has little relevance at present as there are few 4K TVs or Projectors that are not extraordinary expensive, as well as no 4K material available yet. (No decision either on how it is to be delivered to the user)
Effectively the Pioneer becomes a 4K HDMI Switcher, which is all that is needed as 4K TVs and Projectors will upscale to 4K themselves.
Hope this helps
Bill