On Rockstar's Newsire, the developer said, "we have big plans for substantial additions in 2014 continuing Michael, Franklin and Trevor's action, mayhem and unexpected adventures in Southern San Andreas."
Additionally, Rockstar detailed the future of its online multiplayer. A bigger update hits this week, with deathmatch and the race creator beta rolling out. Later in the month, we'll see four Capture mode variants -- Raid, Contend, Hold, and GTA -- which Rockstar will detail soon. Finally, on the subject of online heist missions, the developer wrote, "Heists are currently in development and we are working very hard to get them as polished and as fun as they can be. Stay tuned for much more detail in the New Year."
Rockstar has plenty more to announce for GTA 5 in the future, as well.