A delayed opportunity, for the future. At the moment, we really aren't missing out on much due to its absence. As the article and Tideland point out, it is not yet a net positive.
"WHAT DRIVES US" posted this small video on FaceBook - [not sure if I'm supposed to post that here - if not, delete it] "Traction display in the new 2019 Prius."
If you look outside the windshield in the video, he's on snow, possibly uphill, and the rear wheel drive is engaged because the front drive is slipping. Have to assume this because we cannot see the VSC/Traction lights, but the should be on.