Today's technology does not offer native 4K imaging that delivers the same performance in terms of sensitivity as the best HD cameras available. In addition, native 4K acquisition with 2/3" imagers does not offer global shutter operation a requirement in many of the more demanding applications with high speed movement. Another complication some limitations are optical, and not solvable. HD will be used for many years. Most equipment purchased today will need to be used for both 4K UHD and HD. For now, mixed simultaneous operation might be the best option.
And the questions don't stop there. There's also a decision to be made with regard to 4K UHD transport Quad-SDI or IP. More on that in a future post!