United Front Games isn't working on a Vita version of LittleBigPlanet Karting, the developer's confirmed.
Game designer William Ho told the PlayStation Blog:
Alas, we are concentrating 100% on making the PS3 version LittleBigPlanet Karting the very best it can be. We are not working on a Vita version at this time.
Of course that's not to say there won't be a LBP Karting for Vita in the future, so don't write off the chance of seeing Sackboy in a kart on your handheld eventually.