A few months ago we heard from Slightly Mad Studios who said that the Wii U version of the game was struggling considerably. Perhaps that is why it shouldn't be surprising that the game has now been officially cancelled.
Speaking to Nintendo Life, developer head Ian Bell, confirmed the version was no longer imminent, but hinted we will see what happens with the NX:
The official line is that we're awaiting an announcement from Nintendo on new hardware. As of now pCARS is simply too much for the Wii U.
This isn't that surprising since the Wii U is seriously underpowered compared to PlayStation 4 and Xbox One. Still, I know people who backed this game's Kickstarter specifically for the Wii U version, so it is pretty rubbish to see them come out of this empty handed.