JK Studios is an animation studio and is run by James Kearsley. He had updated his professional career on the JK Studios website (now removed), but you can check it out from the Google Cache. If you notice the resume is listing LittleBigPlanet 3.
This third part would be being developed by Sumo Digital. If you take a glance at that CV, JK Studios had collaborated before with Sumo Digital on Sonic & All Stars Racing Transformed. Therefore, we should take this rumor as right.
Long time ago, Sumo Digital was rumored as development studio for LBP 3. Now, we have got an indirect confirmation for this fact. The question is: LittleBigPlanet 3 will be on PS4 or PS3? Today is the day to unveil these rumors, E3 2013 is warming up.