If you have not played a DK in Legion;
The Ebon Blade has started to raise both Alliance and Horde soldiers at random on the Battlefield against the Legion.
Therefore it makes no sense from a lore perspective that there is still races who can not be Death Knights. Saying the Introduction of DK's doesn't fit on a Panda shouldn't be a problem either as it has not been a problem for Worgen even tho they also are supposed to have a different start in lore than other DK's.
Please make Panda DK's available in a future patch just like gnome hunters and other combinations were enabled in the past so I can race change into a fluffy ball of death and destruction ヽ(◉◡◔)ノ