While its been confirmed for some time now that Nightwolf would be a part of the first Mortal Kombat Kombat Pack, what wasnt known was when the character was going to be released. In fact, with Shang Tsung only recently being released, many had speculated that the next character to join the fight would be the first guest character, Spawn. However according to a recent PC leak and tease by Ed Boon himself, it would appear that Nightwolf will be Mortal Kombat 11 next DLC character.
Source: N4G PC Mortal Kombat 11 Next DLC To Be Nightwolf; Joker, Ash, Terminator and Fujin Leaks Resurface