The Last Guardian, along with Agent, are two PS4 exclusives that have yet to see the light of day since being revealed oh so many years ago now.
The trademark for The Last Guardian has seemingly been dropped due to it not being used, or asked for an extension following a Notice of Allowance sent to Sony. While this doesn’t necessarily mean the game is canned, it doesn’t bode well for the fan-base eagerly awaiting updates on the game. The dropping of the trademark could mean a number of things, including a new title for the game for that matter.
The trademark was abandoned once before in 2012 as well.
The full trademark listing can be found here on NeoGAF. I wouldn’t lose hope just yet for The Last Guardian as there’s been multiple reports over the last couple months that the game was being reworked, so this could have something to do with that as well.