According to VG247 LittleBigPlanet 3 is in development at the moment. The title is being developed by Sumo Digital rather than Media Molecule. Sumo Digital is a developer who previously worked on Nike + Kinect Training, Dead Space Ignition, and the Cross Controller content for LittleBigPlanet 3. The team has reportedly been at work on the title for a little over a year.
This is a rumor for now, but it’s not hard to believe. Since the series started in 2008, we’ve seen many games starring Sackboy. The original LittleBigPlanet was followed by a PSP version in 2009. We saw a second PS3 game in 2011. Last year saw Little Big Planet Vita as well as Little Big Planet Karting. While the specifics of the rumor are still speculation, it seems very likely that another LittleBigPlanet game is being developed.