alt Hacker News> spaceflight is not the place where it is appropriate.
But, a video stream meant for the public consumption is. SI are standardized for the context of calculations, not necessarily for human consumption, which happens to be why nobody gives the weather in degrees kelvin.
Their main target audience is still space geeks. Parts of broadcast will be shown in daily news bits on cnn and reuters, who will still translate the height to football fields, velocity to car speed, etc. Geeks will watch and re-watch it multiple times and fight over crazy theories online and it really helps if you can use normal units of measure.
Btw the rest of the world measure temperature in Celsius which is derived from Kelvin (by adding or subtracting the value of absolute zero in Celsius).