It seems that the rumours that Media Molecule was working on a first-person perspective for LittleBigPlanet were wrong. The game already has the capability to run in first-person.
Speaking in an interview and responding to a question about the first-person rumours, Media Molecule's Alex Evans actually showed the interviewer how the game's levels could be played in not just first-person perspective, but also third-person as well.
There was no official announcement on if we'll ever see the first-person perspective in an official release, but instead was done to show the versatility of the game and its engine.
David Smith admitted incorporating a first-person perspective would be a "radical change" but added: "If it's something that the community wanted, we'd totally listen to that. At the moment there's so much crazy stuff that we could do within this 2.5D context, we'd like to milk that more".