Yes, The Last Guardian is still in development

Meaningful development of The Last Guardian appears to be occurring, according to its creator Fumito Ueda.

Kotaku reports that Ueda, who left Sony in 2011 but 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?

MCV has the full story.