I think they'll wrap up the story of the first game in this (1st) season, they just can't stretch it to a 2nd season 'cause they've skipped through a lot already and they're close to the end of 2nd act. The whole dlc events could be done in a one episode (or less)..
Though they might stretch the TLOU Part II in 2 seasons, since it's long in comparison to the first game, also provides enough gap between it and the 3rd game which is still in development..