It seems the recently announced Little Big Planet Karting isn't coming to PS Vita anytime soon. In a comment to a user comment on the official Playstation blog design director William Ho wrote the following:
"I love my Vita too!
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."
This certainly doesn't rule out the possibility as evident by the fact that another studio () adapted United Front Games' Modnation Racers to the PS Vita.