“The worlds been hard on us…hard on him. Joel’s done some terrible things. He tells me that on this journey, you either hang on to your morals and die, or do whatever it takes to survive.”
— Ellie (The Last of Us)
In the AMA that took place a couple of weeks ago, someone asked if Joel would ever sing to Ellie, to which Neil answered "Will you be at PAX? ".
That could mean just Troy Baker being there, Troy being there and singing to please the audience, or ND showing a teaser for the DLC showing Joel singing. I hope it's the last one.