There isn't really anything to tell. There's nothing about the game out yet, it hasn't been announced by Naughty Dog that it's even being made. The only hint so far is that the name was registered for trademark over a year ago.
Quote from WikipediaOn April 21, 2006, a trademark was registered with the USPTO for "JAK AND DAXTER: THE LOST FRONTIER". The description given for the use of this trademark was "computer game software and video game software" as well as "operating an online real-time game for others over global and local area computer networks".