Sony has said that The Last Guardian is still in development, despite its US trademark expiration.
It was reported this morning that Sony has allowed the US trademark for the game to expire. However, the platform holder has told Videogamer, GameSpot and GameBlog that the game has not been cancelled, although no reason has been given for the trademark lapse.
Back in December the game's creator Fumito Ueda, wholeft Sony in 2011but continues to work on the game, told Dengeki that "talks with Sony Computer Entertainment on The Last Guardian have been ironed out, and we're making progress under completely new conditions”.
Does ‘new conditions' = PS4?
Although the game was pencilled in for PS3 at the time of it reveal in 2009, five years and one console down the line it's surely now a safe best to assume that the game is PS4 (or PS5, PS6 etc etc) bound.